To be honest this is the first time I read someone saying "Tidus is super hated in the West". And I'm a FFX nerd.
I doubt that's the case at all. He has detractors but you could say that for any protagonist in the series, including Cloud, but according to my experience usually those detractors end being people who never tried the game and thus, never properly discovered the main character's motivations and his/her development.
I guess a part of that comes from the infamous laugh scene but as Ivander has said, besides the fact it has become a big meme, the scene has it's reasons to be like that. Of course, without context, seems very stupid and all, but in reality it's kind of a touching scene, at least if you ask me.
As for Yuna getting over Tidus, well, yeah, they would probably pick Tidus first and I wouldn't be mad. I like the character and he could bring some fun ideas to the table (even if for some people he would just be
another swordfighter).
I just mentioned Yuna because I like her a bit more than Tidus and she's as much of a protagonist as him in FFX.
Well the scene wouldn't be as much of a meme if viral videos did include all the context, I guess.
And I completely agree with Tidus being one of the best developed characters in the series. At least, among the protagonists. I guess some people end disliking him irrationally because at first he might seem your usual "haha i'm cool and funny" JRPG protagonist, but obviously there's a lot more than that with him.
Jecht would be a sick pick. He's super badass, that alone would make his inclusion worth it. I loved his playstyle in Dissidia Final Fantasy.
Also, his song is an absolute banger of heavy metal with growls, which would be very unique in Smash lol