The question is, why are you so blind to what makes these films so popular or "the zeitgeist" as you call it? Surely you can see that there needs to be some kind of demand for it, which would explain the impressive growth of the franchise. Transformers is a good example for a successful franchise that lacks quality, but that franshise already started to see a decline in box office numbers after the third film. Calling someone blindly idealistic because they recognize the steady progression and continued success of these films is short sighted. Historically, franchises can't just put out poor quality and see progressive box office results. Star Wars, Harry Potter (or more specifically, Fantastic Beasts), and Transformers are all examples of major franchises that started to see a decline immediately after poor reception to their films.

You seem to be going out of your way to ignore anything positive that may contribute to the success of the MCU. I am not saying every film is a creative masterpiece, in fact I also find some of the films to be formulaic and bland, but many of the films have creativity despite the generalized structure of the MCU films. Maybe the MCU won't hit the highs of Endgame again and they may even have a flop (relative to their own high expectations), but there is no evidence to support the idea that is will die out completely any time soon.