I always thought Khan from the Wrath of Khan was a bit of a"moustache-twirler." An over the top one dimensional bad guy. That really isn't a criticism just more of an observation. Hollywood has many examples of clear-cut, black and white good guys vs, bad guys and in TWOK Khan was a simple bad guy.
I agree. If it hadn't been for the actor, MontalKhan would have long since been forgotten. I think Marcus was much the same. The character himself was not well conceived, but Weller made the best of it. But I think that's the trend with most great cinematic villains. There are very few who start out great on the page.