Alright, I kinda missed the tiers talk but this is something I feel strongly about so, if you like a character but you're not doing that well with them or they just aren't that good, don't give up. If you want to be good, no matter with who, just be determined. I mained Zelda in Melee, Brawl, and I still do in this game. Let me tell you, her moveset design is like practically picked out of a dumpster and forced onto her. She might be better in this game, but she still isn't very good. You can't pity yourself about your character being bad, you just have to work harder to outplay the other player and get into their mind regardless of who you play. Lower tier = more risky to play, simple as that. If you like Shulk but you're having problems against top tiers, just try to learn the matchup more and be more careful. There's no way I'm dropping Shulk or Zelda just because they suck against Sheik, Diddy, etc. Just work around the impossible.
tldr; If you like a character, use them. Skill is what's going to prevail.
I think the gameplay isn't an RPG anymore and it's closer to a hack and slash like Bayo or MGS Rising. lol inb4 it's another final fantasy xiii