Plus, this thread should've been for both in the first place. Part of what makes the Mega Charizards so good is that, barring packing a Frisk user, you can't really know what to expect from it until it mega evolves, and that makes trying to counter it dangerous. Sure, you can make logical inferences about which Mega Evolution they may be using based on their other teammates, but there's no guarantee. If you send in your Quagsire expecting it to stop Mega Charizard X, then you'll have a problem if it evolves into Y and fries Quagsire with Solarbeam. Likewise, if you send out your Assault Vest Goodra to tank a Fire Blast from Mega Charizard Y, but it mega evolves into X, then bye bye Goodra as it eats a Dragon Claw or Outrage on its much weaker defense stat. So the fact that they do have the same base form makes them a bit better by extension, since you don't know which one it may be until it does Mega Evolve, and there's few (if any) universal counters for both.