It's really impossible to know exactly whose to blame. Sure Perlmutter was likely part of the problem, as was the Marve Creative Committee, but I highly doubt Feige and Whedon are blameless in all of this. I mean, you look at the movies that came out post Perlmutter:>Civil War>Dr. Strange>GotG 2>Homecoming
And... I mean, Civil War was good, but Dr. Strange was kinda disappointing, GotG 2 wasn't as good as 1, and Homecoming is filled with changes from the source material that, whether you like the MCC or not, they would have likely kept them from doing. So even with double the budgets, all the actors getting paid waaay more, and no longer having to answer to the Committee, it's not like the Phase 3 movies are leaps and bounds better than then Phase 1 or 2 movies.
We know who FEIGE blames for all of this, but that was an obvious power-play on his part so he would have twisted the facts in his favor to get what he wanted, and Perlmutter is too much of a recluse for us to really get his side.
The only thing we know for sure is that Perlmutter was horrible to work with on a budgetery side of things, but does an actor getting paid more make the movie better? Morale would probably be better, and you wouldn't have actors constantly wanting to quit out of their contracts, but their performances wouldn't necessarily improve just because they got more money.