yes, it is fair, because it's their plot and if a certain character's abilities would ruin the entire plot and not give anyone else the chance to do anything, that's not fair to all of the other people who want to participate.

this isn't an official game event. the player running a player plot has the right to pick and choose what characters get to be involved in it, for example things like the xion plot ages ago where only a certain number of characters got to fight her at each stage. when you play an extremely powerful character, you have to be ready for the fact that sometimes you're not going to be able to participate in things like that for the sake of making it fair for everyone else. otherwise only the powerful characters would ever get the spotlight in anything.