Immortality IS an acomplishment as far as I'm concerned. A gateway acomplishment that can only lead to more. I consider the full story. Only reason one would choose to ignore a continuation is if it made one's case harder to make. But, if you want to argue solely on their original games, yes. Sephiroth did lose. He does sitll however posess greater power than anything else in his world, and more power than other villains. Whether or not he put that power to good use is another thing entirely.

I'll have to go dig that quote up later, got a damned research paper to do now unfortunately.