Those decks can play Arbor Colossus out of the board, and they should be playing it in the board for the mirror anyway. It blocks Stormbreath Dragon forever.Master of the Feast was a SB card last season against GR Monsters because they couldn't get rid of it. It didn't matter that they drew extra cards because none of them would be removal to stop him, and he's so fast that even with the extra card they couldn't win the race.
If a popular deck exists that has no removal (like Reid Duke's GR devotion deck), then that is where you would use it.
Also, Monsters could kill it. Setessan Tactics was in EVERY sideboard.
The had trouble killing Desecration Demon because it was 6 toughness, but Master being 5 means it dies to pretty much every Tactics. DD had to be killed by exactly Poly. Why are you guys trying to make a case for this bad card?