Blaziken was banned more for his Speed Boost + Baton pass shenanigans. He also had access to Swords Dance too which didn't help. Mega Blaziken comes in on something weak to it, lets say Ferrothorn a common wall, forces a switch gets an SD off and then proceeds to go ham. When he's near K.O range he could pass those speed and attack boosts out and then proceed to ham it up again. Those easy and amazing passes are what made him really dangerous. Azumarill and Talonflame, even adaptability aqua jet Crawdaunt to an extent, can handle him really well but thats the thing they need to run them in their team and not everyone liked running them. I don't think Mega Blaziken is all that scary either but then again I always have Azumarill with me...