There's a lot more to Eva than the premise. It's not meant to be a commentary on it, but rather the emotions, mental issues, and other topics treated in the anime, are the important part, and using mechas and underaged kids forced to pilot them in a post-apocalyptic setting was the way they chose to portray it.
Hideaki Anno at his best, it's like saying the premise to the NieR and Drakengard games is that other apocalyptic games don't truly board the reality of a completely lost future, when in reality its real focus is humanism and other philosophical lines of thought with an insanely deep and complex (and well-build, at that) lore, the setting is merely one of the best ways to portray it and make it attractive to people. In short, Yoko Taro being Yoko Taro.
The Yoko Taro thing would be explained better if you say interviews where they ask him stuff. His answers are a big contrast to the complexity and detail of the series and its lore, just like with Hideaki Anno's works, and interviews. They could both give their clear, fixed view on the game and what they want to portray, but their focus is not to explain the setting, because the setting is secondary to the philosophies and messages they want to portray while allowing the players/watchers to interpret themselves from their POV.
They will make a massive work of art and puzzles, and when asked about it, they'll reply "We added X because we liked it, looks cool".