Agreed. I love James Spader as a bad guy, but Ultron is a genocidal robot with Oedipus issues not having a snarky personality. What's made Ultron a great villain is his ties to so many of the Avengers NOT named Tony Stark. Making him a Stark creation instead of Pym while logical given the story line in MCU doesn't work the same way.
I think Kang has only once had a direct encounter with the F4, despite being of the Richards family. He's an Avengers villain almost from the beginning of their very existence and one could argue, they are the reason he even exists.And I see Kang as mostly an F4 villain especially considering the MCU couldn't use him until now.