I don’t think the impression is quite accurate, either. The one thing this may prove is that the highest - grossing of all movies released during a certain time frame have become worse, but that doesn’t mean all blockbusters have. I’d like to see how they chose their movies, too.
We do know that most of the really successful recent blockbusters also were critically appreciated. Avengers, for example.
It’s not Godfathers, of course. I think that’s a fair enough point: there’s are kinds of dialogue - heavy movies that in the seventies used to reach the widest audiences that won’t do that anymore, compared to action-heavy movies.
Either way it’s not a problem. There are more than enough great movies out there that find a big enough audience. There’s room for action spectacles’ audiences being bigger, even those of them that are rightfully critically panned.