Squall X: I agree with your assessments of the other villains, Kefka is another of my favorites, but one could argue that the “psychotic and sociopathic clown” trope is thrown about by and large. I also can’t help but notice that you aren’t giving FF7 and Sephiroth their due. I’ve noticed many JRPG and FF fans either love or hate FF7 and rarely is there a middle ground; FF7 truly catapulted the JRPG genre into the stratosphere and instantly made it iconic - because of this many fans incorrectly claim it’s overhyped, yet it’s the one game the masses think of when they recall Final Fantasy. This is an objective fact.
I found Sephiroth to be utterly relatable as a character. He’s a fallen hero akin to that of Anakin/Vader whose entire life had been a huge lie and therefore mentally cracked. His entire aura exuded menace, sadism, and narcissism - all traits I myself exhibit. He’s simple and almost primitive in his obsessions, and it works because FF7 gave him a platform to thrive in the narrative. Not all villains meet a specific criteria and are all driven by their own abstract notions. Deep complexity and nuances are completely subjective by their very nature, therefore can be exhibited by the most minuscule actions a character takes - what matters is what you perceive to be truth. I do believe that pacing is one of FF7’s greatest strengths, and the way the developers set Sephiroth's character throughout the course of the game is fabulously executed.
Oh, and Sephiroth murders Sidious.