I guess you could say everyone contributed. Even Tidus... I hate to admit it, but he did give the party the motivation to try and save Yuna from inevitable death. And he DOES provoke Yuna and Wakka to think and he DOES act against it all. One could say Tidus is the match that started the fire, I suppose.

I will always have the opinon that the game should have been set up like this though

Tidus' role should have been minimized. I know he has his own link to Sin, I know he is Yuna's love interest, I know he's the star player of the- Wait a minute. Anyways, I think the story should have revolved around Yuna. Not only would she have made a good main character, but her story would have been TEN times better than that of Tidus' alone. Think about it, a sheltered, quiet girl has a big legacy and fate thrust upon her and has to make the ultimate choice of sacrificing herself for a world she doesn't know a lot about. This would have made a GREAT main character AND story. Tidus could still have a role in this. Just minimized compared to Yuna's. He still could have been there, motivating the party with his Blitzball skills and airheaded spirit, still could have fallen in love with Yuna, but he would shut the smurf up about it being his story, and let Yuna do the talking.

To me, the game would be ten times more interesting through Yuna's perspective. I wouldn't mind the occasional character switch and still including stuff about Tidus' backstory either. Just through Yuna's POV. Of course SOME things would change, but it'd be for the sake of the story and Yuna being the lead.

Does he NEED to be in X? I still don't think so. He was annoying, whiny, and as bitchy as I'll get out. I think Square could have easily taken him out and come up with some alternative to him, like having Jecht join the party. But TWO badass guys like Auron and Jecht might lead to OP parties... But if we are talking about taking him outta the game in general, without Square reworking anything, then no. Tidus, sadly, plays a somewhat large role in the story as far as breaking the cycle.