Is GB OP? no
Is he unbeatable? no
But is he a guaranteed win? also no

GB is a challenge to play and to play against. He can lose any game or can win any game.
His blowing strike is portal + plazma + GB ability. Great combo, great challenge yet not guaranteed.
If this is disabled, there would be one less hero in the competition, and one less top tier deck to play.

The game is really balanced with him using portal, do not change that please.