The actor performances in the Marvel movies were surely good. But to be remembered in the annals of cinema history, one can't just be good - one has to be amazing. It's telling that for all the praise Hemsworth and Downey have received, neither of them, nor anyone in the MCU, has been nominated for an Oscar for those movies. The MCU aren't exactly character dramas; they're focused on action. There's not much room to show one's acting chops.