So far post endgame we haven’t really seen critics be any harsher towards mcu movies. We’ve simply seen worse mcu movies (as indicated by a variety of robust non critic metrics as well).
SC and NWH are the two with stellar GA response… and the 2 above 90. Total agreement. Eternals and QM are the only two flat Bs in the entire franchise… and the only two rottenes. Total agreement. WF did well(-but-notSC/NWH-well) with critics, and with non critics. DS2 and L&T were shaky-but-not-as-bad-as-Et/QM with critics, and same with normies.
In infinity saga, there was a pretty strong relationship between critic reception and non critic reception for the mcu — unusually strong, for a blockbuster action franchise. So far in multiverse saga we have seen… that unusually strong agreement continue, basically just as strong as it was before.
There may come a time where that relationship diverges notably. Maybe that time will begin with Gotg3, though there is no particular reason to think so just yet. But until such a time, this “why are critics harsher on mcu now” discourse is absurd, since there”s no real indication they are being harsher at all!