Being a character loyalist means that their placement on tier list couldn't mean less to you. You will main this character no matter what anyone thinks.
I'm a bit of a loyalist freak. I'm loyal to: Ness, Lucas, Mewtwo, Rosalina, Shulk, Ice Climbers, and Palutena. I'm also psudo-loyal to Link and Zelda, except I only play them in the games featuring the Ocarina of Time incarnations. Call me stupid, but it's not the same playing as Twilight Princess Link and Zelda. My reasoning behind it is this. I love playing Smash competitively and analyzing it with a passion. There's nothing else in the world that's quite like it. However, amongst all of the analyzing and testing, I think that we tend to forget that Smash is the legendary battle of our favorite video game characters.
For example, to me, Ness isn't just a projectile based moveset with an amazing back throw. He's the PSI powered leader of the Chosen Four, who managed to visit the Eight Sanctuaries and defeat Giygas, the embodiment of evil, even when all hope seemed lost. For me, Smash is supposed to be about fighting as your favorite character. That's how I've always played it and that how I always intend to, even as a competitive player. I don't want to play as a moveset. I want to play as a character. In my mind, if you're into picking the best characters in the game, then great! Do that! However, I've always enjoyed Smash more when I play as a character I love. The only "exception" to this rule is Ice Climbers, since I don't like them because of their game. Instead, they were my very first main from way back when I first played Melee and, as a result, they'll always have a special meaning to me.
Well, that's my cheesy rant on character loyalty. Also, one final thing. Character loyalty doesn't make you any better than people who just pick characters because they're good. So, don't go thinking you're better than someone who dropped Diddy the moment he was nerfed because you've played the same character since day 1.