OK, so you failed to answer my question. Is that world actually a possible world? How would you tell?
The problem with 'greatness' is that there are many different properties by which to measure it, and they can all give different answers. This means that you do not have a linear order (where every two things can be compared), but what is known as a partial order (where some pair of x and y, x is not greater than y nor is y greater than x).
Also, I know of a number of different axiom systems for math that can give mutually contradictory results. So which particular axioms for math do you use? And why do you think those are the only possible ones?
But even more: there are multiple different systems of *logic*. The most commonly used one is Boolean logic, but Heyting logic is also useful at times. It is possible to have multiple valued logics, for example.
I would read up on this. I try to help you here, but you are trying to make confusing what is very simple. Possible world just means what is logically coherent. Math, Logic, whatever the truth of those are, they are consistent in all, and necessary truths. This doesn't mean we grasp all of it properly.