Can A Single Argument Prove the Existence of a God?

There appears to be one argument from history by which philosophers and theologians attempt to establish the existence of a God from its very definition, so to speak.

Anselm of Canterbury essentially argued in his Proslogium that:

1. It is a conceptual truth (or, so to speak, true by definition) that God is a being than which none greater can be imagined (that is, the greatest possible being that can be imagined).
2. God exists as an idea in the mind.
3. A being that exists as an idea in the mind and in reality is, other things being equal, greater than a being that exists only as an idea in the mind.
4. Thus, if God exists only as an idea in the mind, then we can imagine something that is greater than God (that is, a greatest possible being that does exist).
5. But we cannot imagine something that is greater than God (for it is a contradiction to suppose that we can imagine a being greater than the greatest possible being that can be imagined.)
6. Therefore, God exists.

Instinctively, you could think of this argument as being driven by two primary ideas. The first, expressed by Premise 2, is that we have a coherent view of a being that exemplifies all of the perfections.

Otherwise put, Premise 2 supposes that we have a cohesive view of a creature that embodies every property that makes a being superior. Other things being equal than it would have been without that property (such features are also known as "great-making" properties). Premise 3 asserts that existence is perfection aka a "great-making" attribute.

Respectively, the exact notion of a creature that typifies all the greater attributes implies that the being exists. Assume that B is a being that represents all the perfections and assumes B does not exist (physically).

Since Premise 3 implies that existence equals perfection, it follows that B lacks a perfection. However, this contradicts the presumption that B is a creature that embodies all perfect characteristics. So, in line with this reasoning, it follows that B exists.

Question:

Does this argument prove a God exists? Why or why not?