>>43529990It's fair because anyone can have a Mega Rayquaza. Even if it's absurdly powerful, you can bring your own.
Meanwhile, Phione is a massive pain in the ass to get, since you need to get a Manaphy which is only available at obscure events or from a copy of Pokemon Ranger (with only one Manaphy ever being available per copy).
VGC may be a mess where the number of viable mons can be counted on your fingers, but at least you can be sure that your opponent will never send out a mon that you weren't able to get your hands on.