Not to put to fine a point on it ... but Brie Larson has an Academy Award (aka, Oscar), a SAG Award, a Golden Globe, and a BAFTA, among other awards.
If you don't think that she is a great actor, then I am not sure who could possibly qualify. Again, acting is somewhat subjective* ... but I can't help but notice that there is a certain .... common approach ... that you are taking when you are dismissing some people's acting, and accepting others.
The entire point of this is, of course, that the issue with Marvel isn't on the acting side. In addition, I will reiterate that success (in terms of metrics) and quality can be related, but are not the same thing. You can't just cherrypick random things to support you, and disregard counterexamples. You also shouldn't be comparing across different media- TV and films are quite different; something Marvel is learning.
*Brian Cox is a great actor ... but most importantly he was given a great role in Succession. If you were familiar with his filmography, you'd know that he's been in more than his fair share of stinkers