Oh no, I love Seifer, and I love every scene he's in. The problem is he's cool but pointless to the story. You could have taken him out of the game altogether and it wouldn't have had much of an impact on the way the events played out. Like you say, he's a perfect rival....but there is never any actual rivalry related plot-threads in the story using him. Squall gets his scar, and then Seifer spends the rest of the game being cool and not really contributing much to the story. Seifer should have been like Rufus from FFVII. He wasn't the main antagonist, but he still had a major role to play throughout the story.