Why cant we see a sickened old gangster fat guy
..Don Corneo...
or a small cocky dictator like Hitler
...President Deling, President Shinra...
These characters work well as less-than-ultimate opponents. They have power, but its all financial and/ or political. Besides, there are too many of them in THIS world, without shoehorning even more of them into fantasy worlds.
"Macho style" usually equates to brawling meat-headedness (Duke Nukem et al), completely devoid of intellect and magic - two key components of FF villains, due to their universal intent to obtain limitless power and the ability to transform into a powerful winged thingy when confronted by their nemesi.

'Smooth' opponents such as Sephiroth have a look of precision yet are also outlandishly unconventional. Refined but unconcerned with what the 'mainstream' tolerates. They're strong enough, in every sense, to simply not care. I agree that Kuja looked marginally absurd; the same however could be said of most of FFIX's cast. I'm not familiar with Seymour so I can't comment, but Sephiroth wasn't exactly 'androgynous' at least he wasn't any more so than Cloud or any other anime-styled hero.

Take a look at Laguna... he matches the image stereotype you mentioned. He's a hero, of course, yet you often refer to his nack for destroying womens' lives, and you've also described him as having 'infernal powers'. Something to think about, in my opinion...