I don't think what was established in MOS is a "Gritty/Grounded/Realistic" universe at all really. But it was a universe of "consequences". If an alien with awesome power that looked like us were raised on Earth, what could the reaction be on this planet? What would be the consequences? Jon Kent in the film was guided by that idea and his fate showed how those consequences played out in a personal way for Clark. General Zod is the last remaining invader and there is no way to send him to the PZ, and he wants vengeance on Kal-El and Earth. What are the consequences? But other than some off the cuff explanation (about as detailed as what was done in Thor, which is to say, not that detailed) from Jor-el we don't get some technobabble timey whimey rationale for Clark's real world impossible powers. As long as a WW story is about the consequences of her existence in the world it really doesn't matter that her origins are tied to the magical power of ancient gods.
Do you think magic powers can work in the context of a film like Terminator?

) is going to balk at seeing the Amazing Amazon Warrior Princess standing next to Atlantean King and the totally humanoid alien we call Superman. As long as it's consistent on a dramatic level the DCCU does not need some UNIFIED FIELD THEORY of superheroes.
) And would you be willing to go along with that, buy tickets and other products, financially support this take, just because a WW film came out first in which her origin is her classic one? Would you agree with the rationale that if you want a film with both those heroes in it, then Superman's origin must be sacrificed? If your answer is NO, then why would it be any more acceptable for Diana?