In case Megacham does not get banned, it would have a niche as the Pokémon that can stand a chance during the first turn (Fake Out)... if one did not realise its HP and Defence are 68 and 65, respectively (before Mega Evolving). This means that...
252 Atk Pure Power Mega Medicham Fake Out vs. 0 HP / 0 Def Bibarel: 110-130 (36.7 - 43.4%) -- guaranteed 3HKO
252 Atk Pure Power Mega Medicham Fake Out vs. 0 HP / 0 Def Gallade: 104-123 (37.5 - 44.4%) -- guaranteed 3HKO
... a Bibarel has better defensive capabilities. Bibarel.