The argument equivocates between premises 7 and 8, on the concept of unbounded.
Let me ask you some simple questions.
If God has all perfections, relevant to God´s divine nature ,how many perfections more Can God have?
If a being, has all perfections, relevant to God´s divine nature, , minus one perfection, how many more perfections ( of the same kind) can that being have?
Is having all perfection, in the sense discussed, here, bounded or unbounded?
PS: plausibly, premise 5) is false. A probabilistic measure with an exponential distribution is a measure of unbounded set that has a maximum measure (namely, 1)
In answer to your questions:
"If God has all perfections, relevant to God´s divine nature ,how many perfections more Can God have?"
Answer: It's a meaningless question due to the incorrect use of language. It is not possible to speak of "all perfections", because the word 'perfection' is defined as: the act of perfecting or the state or quality of being perfect (this is from the 5th edition of Collins English Dictionary, but I am sure you will find that other dictionaries will concur with this definition). There is no such thing as "a perfection" or different perfections. What I think you are trying to ask is: "If God has all perfect qualities, relevant to God's divine nature, how many perfect qualities more can God have?"
The problem with this question is that nothing is defined. What exactly does "relevant to God's divine nature" mean? The term seems to imply some kind of limitation, as if to suggest that there are "perfections" (which, as mentioned, I take to mean "perfect qualities") relevant to God's divine nature, and theoretically "perfections" which are not relevant to God's divine nature. If all "perfections" are relevant to God's divine nature, then it follows that "relevant to God's nature" is a necessary condition of any "perfection". And thus we are dealing with a circular argument. Thus possession of all perfect qualities is a definition of God's nature. It would, of course, follow from this, that no perfect quality can exist which could be added to God's repository of perfect qualities, so it would seem that God possesses what is vaguely termed "maximal greatness".
However, we need to understand what the concept of 'perfection' means. Perfection has to do with exactitude, completeness and the absence of flaw and corruption. So we have, for example, a perfect circle. But
all circles are, if truly 'circles', in principle 'perfect'. We may see, say, a drawing of a circle, and we discern that it is flawed. We say that it is not a perfect circle. This is just a convenient way of speaking, as we can see that the intention of the artist was to represent a circle. But, strictly speaking, that artist has not drawn a circle, but another shape which is said to be an approximation of a circle. The 'circle' concept which this shape approximates is the idea of a perfect circle in the mind of the observer which is, so to speak, imposed on the image and the judgment is made that the attempt by the artist is sufficiently close to the ideal, as to warrant the description of a 'circle' for all practical purposes. There is only one circle, namely, the perfect circle, and all human attempts to represent that idea are flawed to some degree. Therefore there is no such thing as a qualitatively 'maximal' circle, as if there is a hierarchy of genuine circles with the 'maximal' circle at the top. Only one "circle concept" exists, and all human representations of that "circle concept" are mere reflections of this perfect idea.
In the same way, there is only one "goodness" - namely, God's goodness. There does not exist a hierarchy of "goodnesses". Whatever goodness exists in creatures, is merely a reflection of this one perfect goodness, which comes from God. The same applies to the ultra-vague term "greatness". Therefore there is no such thing as "maximal greatness". There is simply the greatness of God reflected in man, distributed among human beings, and usually corrupted by them.
I suppose it is possible to use the word 'maximal' to describe the idea that
everything of something pertains to the one who is said to be "maximally something", in the sense that when he distributes this 'something' to others he is not losing anything, but still retains possession and control of it. This is just semantics. It is like saying that the sun possesses 'more' light than the moon, even though we know that the light of the moon is actually the light of the sun anyway. The comparison is merely a matter of perception. Objectively the sun possesses more light than the moon only in the sense that something which is full possesses more of the thing of which it is full than the thing which has nothing at all. One could say that the sun, with respect to the moon, is "maximally luminous", but really this is no different from saying that the sun is merely luminous and the moon is not.
Thus in the same way, to say that God is "maximally great" is to say no more than "God is great", and nothing else is great other than God. Whatever greatness creatures possess is merely a reflection (albeit possibly corrupted) of God's greatness.
Therefore the ontological argument is irrelevant. It relies on comparison to claim that existence is a great making property. What the argument should be trying to do is simply argue that existence is a necessary condition for 'greatness' per se, whatever the degree of greatness. But this gets us nowhere in trying to prove the existence of God, because we are merely in the domain of defining terms. If existence is a necessary condition for greatness per se, then it must also be a necessary condition for reflected greatness. In the same way, if the action of photons is a necessary condition for luminosity, then it is necessary condition both for originated light and reflected light. Thus any 'reflected greatness' (such as the greatness of a character in a work of fiction) should possess the quality of existence. And my example in parenthesis shows that this cannot be the case.
The idea of 'maximal greatness' when applied to God is incoherent, as I have explained, and existence cannot be a necessary condition for greatness
unless only non-fictional beings possess greatness. This is, of course, begging the question. If only non-fictional beings can possess the quality of greatness, then how do we define 'greatness'? If greatness necessarily includes moral qualities, and we are forbidden from applying such qualities to fictional characters, then how can we even talk about such qualities? (Jesus certainly did in the parables!). If we can apply such moral qualities to fictional characters, then these qualities cannot be a necessary part of the definition of greatness. So what therefore would be left of the definition of 'greatness'?
Now I suppose one could argue that even though there is only one 'greatness', namely, the greatness of God, it must exist in order for it to be distributed among both non-fictional and fictional creatures. I certainly agree with this. But this relies on
other arguments for the existence of God. Greatness exists. It comes from God. Therefore for greatness to exist, God must exist. This is based on the premise that greatness comes from God (assuming we all agree on a definition of 'greatness'). If we can prove that greatness comes from God and that greatness exists, then we have proven that God exists. This is really no different from saying that design exists, design comes from God, therefore God must exist. This is not the ontological argument. We are simply looking at aspects of reality and arguing that these can only exist if God's exists. It is
a posteriori argument.
"If a being, has all perfections, relevant to God´s divine nature, , minus one perfection, how many more perfections ( of the same kind) can that being have?"
Answer: This question is really a variation of your first question, reliant on your definitions (which I dispute), and therefore it is covered in the answer above.
"Is having all perfection, in the sense discussed, here, bounded or unbounded?"
Answer: perfection is, strictly speaking, bounded. Perfection is itself a bound. But the discussion concerns the idea of
comparison. As I have explained,
objectively speaking something is either perfect or it is not. If it is not, then the imperfect thing is really something else and not that thing at all, but is another entity operating as an approximation of the perfect entity. It is a signpost pointing to the perfect entity. Therefore there is no such thing as 'maximal perfection'. There is either perfection or imperfection. Thus, perfection is 'bounded' by its own definition. That is not to say that there cannot exist an infinite expression of something perfect, but the thing itself is merely what it is.
"PS: plausibly, premise 5) is false. A probabilistic measure with an exponential distribution is a measure of unbounded set that has a maximum measure (namely, 1)"
No it is not false. I stated that "There is no maximum measure in an unbounded infinite set". I did not say "in a partially bounded infinite set". Such sets do indeed exist. The set of all real numbers between 0 and 1 is a bounded infinite set, of which '1' is the maximum number. I wrote "unbounded infinite set". Perhaps I did not make this clear enough.
Finally....
The modal OA draws a distinction between "possible world" and "actual world" and correctly argues that the actual world is a possible world. By saying that the actual world is a possible world and that a maximally great being exists in every possible world, it concludes that God exists in the actual world. There is a huge problem with this, and that is the problem of inconsistency.
If the actual world is a possible world, then why could we not say that a "fictional world" is a possible world? If we conclude that God exists because He must exist in the actual world, it being a possible world, then honesty requires us to conclude that God also does not exist, because He must exist in a fictional world, it also being a possible world. Thus we must conclude that God both exists and does not exist. This is absurd, of course.
If we try to argue that a fictional world cannot be a 'possible' world, then we are saying that ALL possible worlds are potentially actual worlds under a particular definition of 'actual'. How then is 'actual' (i.e. reality) defined? According to what criteria or what laws? Could 'reality' be defined in such a way as to include a world which is nothing more than a world of ideas? And if not, why not? If we already presuppose what "potentially actual" means are we not resorting to some element of
a posteriori argument? Does this not then invalidate the OA?
I am certainly convinced that God exists. But NOT (even in part) because of the OA.