It's less about the right villains and more about the direction they are taking their villains... Ultron is a pretty dope villain that was ruined by Whedon's need to stuff a quip in every other word.
MCU just doesn't put a lot of emphasis in building villains... Loki succeeds because he's fun to watch, not that he's a good villain.
It's fine, I enjoy the movies despite that and it clearly works with the fans, but I would appreciate better treatment of their villains because if they had Doom, what's to stop them from treating him like every other villain they have?