I vote no.
I have been playing Welch during 6 months at least, so I know very well how it works. Recently, I changed him for a more "normal" coach (Remi Ercolani), and surprise: I cant't win anymore against Welch setups, or power setups I used to win against (I won't talk about volley setups, I don't know these enough).
So yes, I think that Welch IS overpowered, but I you want to ban him, You have to ban 98 power-service setups too which is very, very, very restrictive if you add it to the coaches already forbidden (Peto Chesire, Jon Samala, Pei Jinq Quah, Aja Golakov).
And then, there would still remain coaches better than others, etc etc...
(Personnally, I would only ban PJQ).
To conclude, I would say there are already too many coaches forbidden on ITST. I you really want to make it fair, you would to have to authorize nothing but SIM tournaments.
TOP SPIN IS JUST A GAME, NOT REAL TENNIS