In general, I think there really isn't anything wrong with wanting to main a low tier.
Smash is fun, but if you try to main a character you do not enjoy, then it can be a real struggle to remain motivated to continue playing. If you REALLY like a low tier, you shouldn't feel like you have to main a high tier. Winning is fun, but if you don't enjoy the game that win feels hollow and unsubstantial in comparison.
Now, I do think people should try out some characters (particularly if they main a low tier) to learn and improve. For example, in melee I LOVE Zelda, she is fun and has a lot of flashy (albeit bad) moves, but she also has TERRIBLE movement and a bad grab. I come from the Rivals of Aether community, where movement mechanics are a bit different and grabs are nonexistent, so while I LOVE Zelda, I currently main Marth because Marth forces me to get good at the things I'm not used to, while still being able to utilize some of the more spacing oriented aspects of Zelda that I like.
But you know what? I still love Zelda, and just because I main a high tier doesn't mean I can't bust out Zelda once in a while or in specific matches, and there isn't anything wrong with wanting to do that for any character in any game. You shouldn't feel like you have to abandon a character you like just to have a good chance of winning, but if that is the case then you also can't blame your character for any losses. You made the choice to play a character that you love, and while them being bad isn't your fault, it is something you just have to learn to deal with.