7. Flag-Smasher - The Falcon and the Winter Soldier was good as a whole but Karli Morgenthau was the one character who felt underdeveloped and they had a perfectly complex antagonist with John Walker's decent from Captain America to U.S. Agent
6. Infinity Ultron - What If...? started as a fun series of episodic stories and I think it worked better that way. Ultron doesn't get introduced until the end of episode 7 and the fiinal episodes just show him as a genocidal maniac with no character , not even the Iron Man like humor that made him memorable in the films
5. General Dreykov - Black Widow was a good spy film that allowed us to see Natasha Romanoff's life and family outside of the Avengers. General Dreykov is a despicably slimy villain with all the depth of a one-off James Bond villain however based on the structure and feel of the film I think that was intentional
4. He Who Remains - This has more to do with the impact on the future than the villain himself. Loki was impressive and funny the whole way through but it took to much time building up the mystery of the Time-Keepers as the villains that when they revealed it to be someone else that they only had 40 minutes to work with him and the only reason we are excited is because he is a variant of Kang the Conqueror
3. Agatha Harkness - This is mainly down to performance as Katheryn Hahn is clearly having the time of her life playing both the quirky neighbor Agnes as well as the insane Wicked Witch-esque Agatha Harkness and her spin off has the chance to give her some proper development.
2. Ikaris - One of the most complex villains in the MCU as he is only doing what he has devoted his 7000 year life to and can't accept the idea that it was wrong. Ikaris doesn't want to kill everyone on Earth he just knows it will be a byproduct of the Emergence and as far as he's concerned one planet is not worth saving for sake of a thousand planets being created.
1. Mandarin - This is a former villain who became a family man and when his wife died he went back to the only other life he knew. His motivation throughout the film was centered on bringing the family he once had and ruined because he refused to accept the fact that his wife is dead probably partly because he was immortal