I think most people could become moderately successful with almost any character. Obviously some characters will hold you back more than others, but if you want to play a character who happens to be low tier, go for it. The only thing I will say is that most people simply don't have fun playing low tiers. People like to focus on how bad they are, but a lot of the reasons they are bad are also reasons most people don't enjoy them. You are really limited in a lot of scenarios. Sometimes you will only have your 1 or 2 options and neither works when the opponent knows what they're doing. If these types of checkmate scenarios won't aggravate you, maining Kirby or Pichu will be fine.
The other main drawback to maining low tiers is people legitimately will not want to play you. Most players will consider practicing vs. you a waste of time outside of tournaments, and even those more open to it will often just want to try out their own secondaries/low tiers because they aren't taking you/your character seriously.
If being technical is the only reason you're considering low tiers, you sort of have to realize that every character can be played very technically at a high level. No matter who you play, if you want to do things that are generally good or effective, you'll need to build up good hand-eye coordination and precision, no exceptions.
