During the early phases of the MCU, the notable exception was Loki, who would be labeled as Marvel’s best villain before he finally got some competition.
Apparently, Marvel knew early on that it had to nail Loki, and executives told Thor screenwriter Zack Stentz that his top priority was making Loki as good a villain as Magneto.
One of the strongest criticisms of the MCU for a long time was that it had a villain problem.
Despite producing iconic heroes left and right, Marvel Studios could never quite create a memorable villain.