Seymour lacks the depth and respectability to be placed beside the likes of Krelian. Krelian is quite possibly one of the greatest antagonist ever written in an RPG and his motive and character are far better explained and justified than poor Seymour.

The main thing that I feel truly makes them different is the fact that Krelian redeems himself. He goes to be with God(WE) cause he knows that he has done too much to deserve living in peace with Fei and Elly. Seymour suffers the fate of most FF villians and becomes a victim of his own ambitions.

But I do agree that Seymour is more like Grahf who was another misguided soul. Yet once again Grahf at least becomes aware of his mistakes and sorta've redeems himself at the very end.