I went 10/0/5 last season as Sion support. Had a 15.0 KDA on Sion for the longest time.
Doesn't mean he was good for the role.
There's nothing Taric does that a different champ doesn't do better, and he's INCREDIBLY susceptible to poke if the other support is decent. Taric is one of the weakest champs in LoL right now. He offers a very one-dimensional targeted stun and virtually nothing else except a bit of damage(but less of it than other champs who offer cc).
Yes, if you're good at a champ, you can win with it and do well... hell, there's that guy who was(maybe still is) diamond 1 who played teemo in EVERY ROLE and, except when it was banned, that was all he played. Didn't mean it was a good choice, but it worked for him.