Nothing should make a character bannable IMO. Now I fully understand that some characters are higher “tiered” than others and there are some characters that someone who’s never played the game before can use and beat seasoned veterans with but that doesn’t make the character unbeatable, nor does it constitute an unfair advantage.
Each and every character has weaknesses. This is true of every fighter game since MK1, if not earlier. If you aren’t good at one character, try a different one. If you suck, practice more. The ability of a character to be unbeatable or “MONSTEROUSLY POWERFUL OMG WTF WE HAVE TO BAN IT NO FAIR HAXS!!!1!1one” is 100% in your mind.