Personally speaking, I am rather positive about this attempt to incorporate everything (even stories which belongs to the 1950s and couldn't become part of modern continuity in any possible way) into one timeline. Maybe it's because it strongly resembles and old fan pitch of mine (I had imagined Superman as a Planetary-like character, arriving to earth in the 1930s and living the most important global events through an entire century). It's all in the execution, of course, but it has more potential than any retelling of Superman's origins we have had in the latest decades (including Birthright).
Also: it is something new. I mean, we have had Supreme and Planetary, but as far as I know this is the first time they have tried to do it with Superman.
As for Superman not being the first superhero in-universe, well, it is not that important and never was. Superman being the center of the
spoilers:
end of spoilers in Doomsday Clock is equally irrelevant. It's like Superman getting a medal for his past glory without playing a central role in the universe he lives in.
As far as I remember, Wonder Woman has several recurring nazi villains, while Superman doesn't have any. It just makes sense that she is in World War II.