Avram:
I would say the steps slightly differently
1)Hashem is in reality either A (corporeal) or B (incorporeal)
2)There is a machlokes in this matter
3)It is not possible to KNOW which opinion is correct
4)It is not possible to absolutely believe that a certain side is correct because the other side might actually be right
5a)Either everyone who ever held the wrong belief is a kofer including Roshonim and including us
5b)Or everyone who held the wrong belief BECAUSE they had no way of definitively determining the truth is excused
6)The Rambam obviously holds that these things are pashut enough that there are no excuses, but for us once there is a machlokes, it is not pashut
7)Some people say that whichever side became accepted must be right because H’ wouldn’t let kefira become accepted
8)I object to step 7 because if you hold like 5b then it wouldn’t matter if kefira became accepted because we would be excused anyway and if you hold like 5a then the same way that H’ allowed earlier generations to be kofrim, he can allow us to be kofrim
9)Because of step 8, step 7 does not have to be true. Once it does not have to be true then we are by definition back to steps 3 and 4 and therefore either the Rishonim/Acharonim who disagreed with the Rambam were kofrim or everyone is excused. You can’t say that they were excused but we are not.
Feel free to dispute my logic. But if you do please explain why you disagree. (All my above steps do not apply to something about which there is an unequivocal tradition in which case we don’t have any sfeikos).