Most of the villains in UF are just plain crazy, self-obsessed, or have some sort of joke philosophy like Church of Man or Objectivism. No one rational opposes the heroes -- or if they do, they eventually end up joining Team Hero like Carmela Sunderland or Liza Broadbank or even freaking GENOM.

"Darth" Venger talks the talk, but still ends up doing the stupid, short-sighted things for vengeance or rage. Clarissa Broadbank's malice is matched only by her pettiness, and that pettiness leads to some stupid decisions indeed. Akio has only been an annoyance so far because he always plays the long game, and because a lot of his accomplishments have been off-screen. Akio tempers the pettiness and rage and pride with the desire for power and his plan to actually achieve that power.

Much of what Akio has done after S2 has been along the same lines as what Utena has done: establish oneself in a new plane of existence, get a new powerful title, pal around with deities, get an academy named after oneself, sleep with a guy who also had sex with Nanami Kiyruu*, marshal a group of powerful fighters, build a coalition with a Force-using order whose goals tangentially match your own (and then refocus them to match your own beliefs). This parallelism is largely the point -- Akio is the Dark Prince to Utena's Light Prince. And saying that he isn't a credible villain is almost like saying Utena isn't a credible hero.

When Yoda made that comment about Utena having the power to crush the galaxy beneath her feet -- that's basically what Akio would have done in her absence. And he continues to plan to do. Right now he only comes out for no-risk, win-win maneuvers, because you always protect your king in chess. Utena's ability to sacrifice herself is where she shines, and will probably make the difference in the end.

Honestly, I wish UF had more villains like Akio, because most of them are idiots who seem like they never really had a chance of success. When his plan finally goes into motion, it will be as hard as hell to stop.** And I'm looking forward to seeing it.

-- ∇×V
* A thought I'm sure you could live without >:)
** Literally