tee bee aitch, I think that we, as a culture, have collectively forgotten that before The Avengers came out, average people didn't really care that much about the MCU outside of Iron Man 1.
Fans project the idea of them being amazing and mostly good, but they're a mixed bag and really just only slightly more consistent than any other long-running film franchise.
Current MC scores for this movie landing in just about the middle of this pack, which is a pretty good rating for a blockbuster.
Anyways, it all comes down to whether the reviewer is rating something by blockbuster standards or by regular movie standards; I think a lot of the higher scores really come down to people being impressed by a movie compared to other big popcorn flicks as opposed to whether it's legitimately good. I would say Ignatiy Vishnevetsky's review at AV Club is a review by a Serious Critic that didn't really let franchise and audience considerations color his feelings about the film, whereas some AVClub reviews in the past might be more sympathetic.
Also! Caring about reviews is dumb because everyone has the ability to consume or not consumes things and form their own opinions, and we shouldn't have personalities based on liking or hating big corporate products