That's bullsh*t. If there is a highly skilled player that is dedicated enough and has enough of experience with the game, then it is possible. Kura getting second at Nats with Talim, and Omega getting top 8 at Evo with Zas already proved this.
Just like how there are people who like to minimize how much they have to think by using Amy or Hilde, there are also some people who actually prefer to be forced to think 10 steps ahead of their opponent by using a low tier character. It gives a greater sense of satisfaction from winning, and provides more room for self improvement.