The Marvel Cinematic Universe has a perfect record of "Fresh" scores on Rotten Tomatoes for every single movie they've released since Iron Man, but the percentage on the Tomatometer doesn't always reflect the actual critical rating. Since the Tomatometer is meant to indicate common sentiment, but not level of enthusiasm, all reviews are reduced to a simple thumbs up or thumbs down, with the Tomatometer indicating the percentage of reviews that are overall thumbs up vs thumbs down, regardless of the degree of the ranking.
Of course, all ratings are subjective. Rotten Tomatoes is famous for giving some audience favorites rotten scores over the years, and even the idea of Tomatometer consensus itself is a bit of a misnomer because the critics that make up that score don't always agree either, with the Tomatometer forcing a consensus by reducing all reviews to a binary positive or negative indicator, removing any nuance from the score. As a result, some movies end up having average critic scores that are drastically different than what the Tomatometer shows. This is especially true with polarizing movies, such as Joker, which has a much higher critical average than its Tomatometer would indicate, especially with Rotten Tomatoes' "Top Critics," where it only scored 49% despite an average score of 6.7 out of 10. This means just over half of critics indicated their score was negative, yet the average of the negative scores was only low enough to drag the average of the enthusiastic positive scores down to 6.7, which is still a considered solid score.
The MCU movies tend to have some difference between the Tomatometer and actual critical scores (as do most movies), although nothing quite as severe as Joker, and none of them have a lower Tomatometer score than average critic score. Only the Top Critic scores for The Incredible Hulk and Thor: The Dark World sport a Tomatometer score lower than average critical score, although both scored higher when factoring in all critics. Even so, The Incredible Hulk and Thor: The Dark World's Top Critic Tomatometer and average scores are closer together than most of the MCU. The MCU movies with the most disproportionate Tomatometer and the average critical score are Iron Man (94% vs. 7.7/10), Thor: Ragnarok (93% vs. 7.6/10), and Ant-Man and the Wasp. Adjusting the average critical scores to a percentage reveals the Tomatometer overrating each by 17 points, much higher than the MCU's average difference of 12 points.
Of course, part of this is simply due to math. For example, Iron Man has one of the highest Tomatometer scores in the MCU and also has one of the highest average critic ratings. Thor: Ragnarok is only slightly below that. Also, a drop from 94% or 93% is still a really high critic average. Ant-Man and the Wasp's Rotten Tomatoes score, however, comes in at 87%, so the 17 point drop to 70% critic average seems like a far more drastic difference proportionally, since 87% is pretty strong, while 70% is pushing into more mixed territory. Interestingly, Top Critic scores for these movies aren't any more divided than all critics, with a 17 point difference remaining the most extreme, while the average difference for Top Critics is 9 points. Thor: Ragnarok is the only movie with that level of division for both Top Critics and all critics, joined by Spider-Man: Homecoming, Doctor Strange, and Spider-Man: Far From Home for that category.
Of course, scoring is all subjective in the first place, so in this context, being overrated by the Tomatometer doesn't mean the movies aren't as good as people say, it merely means the actual ratings don't match the Tomatometer score. It may just be a simple quirk in the Rotten Tomatoes formula, or a peek into a more nuanced perspective of what these scores represent. The Tomatometer may provide a clear ballpark of critical consensus, but it'd also be interesting for the platform to present additional score data in a more prominent way to reflect a slightly less binary approach to film criticism.