Personally, I think Yu Yevon is the villain of FFX, Seymour is merely the antagonist, like Gilgamesh, the Turks, Beatrix, Riku and Ritz. The only major difference is that he doesn't switch to your side, which would have completely ruined his character.

An antagonist is a character or group of characters, or, sometimes an institution of a happening who represents the opposition against which the protagonist(s) must contend. In the classic style of story wherein the action consists of a hero fighting a villain, the two can be regarded as protagonist and antagonist, respectively.
Contrary to what some people commonly believe, the antagonist is not always the villain, but simply those who oppose the main character.
One of the main conditions of being a villain is that they have to know that they're evil, which Seymour fails to fulfil decisively.

Quote Originally Posted by Wolf Kanno View Post
Seymour is the lamest villain in the series by far cause he is irrelevant to the plot of the game he's featured in.
The same could be said for any of the antagonists I mentioned, except for Riku.

His crimes are weak compared to what every previous villain and even compared to what Yu-Yevon/Sin was doing in his own game.
That's what antagonists do. They let the villain do all the crimes. Though Seymour has a pretty impressive list for an antagonist.

His motive was lame
Compared to stuff like:
"I'm enslaving the world because I hatehatehateHATE you!"
"If I can't exist, then I'll destroy all the universe!"
Seymour's motive, to send all of Spira into a spiral of death to end their suffering, is very deep.

If you mentally remove him from the game you quickly realize that it hardly alters the plot in any significant way.
That is a feature of most antagonists. Imagine FF7 without the Turks, FFTA without Ritz, etc.

He was practically the game's "flunky" villain, every time he shows up it's like...

Seymour: I'm here to smite these cause I'm crazy in the membrane!
Party: You again? (party bitch slaps him out of the way and proceeds to continue the plot)
Seymour: I'm here again to smite thee!
Party: WTF!? Didn't we kick you ass already?
Seymour: I'm different now! I'm ZOMBIE SEYMOUR!!!
(Party proceeds to bitch slap him out of the way and continue the plot... rinse, repeat, ad naseum...:rolleyes2 )
Sounds like Gilgamesh, the Turks, and Riku Replica from CoM (without the zombie part) to me...