Has the fighter pass been worth it? I'm debating about getting it now
Yeah. Even if you don't much care about the characters (like, I stopped caring about Banjo back in 2007 or something), those characters are all really really fun to play, well designed (I keep saying this, but imo, since Smash 4 DLCs, Sakurai has been designing the best Smash characters, everyone he makes is fucking awesome nowadays), and even the stages, who have been mostly meh since Brawl, are all good ! Not just fine, but actually good. The best stages since Melee. (The Castlevania stage in base game was also already really good imo).
Also, if we ignore Dragon Quest shitty musics, all the remixs are fucking good, and the amount of music coming with Terry is insane. Like, I think only Mario and Zelda franchises have more music than him in Smash ?
Honestly go for it. If you like Smash, it's a must have. Characters looks good, they put a lot of love and fan service into them, they're super fun, and it's just simply more Smash. Ultimate is the best Smash has ever been, more of it is a blessing.