Idk how far Meta-Ridley scales above his 5-B feat, but by numbers alone Mega Ray has around a 3.3x AP advantage, which is even higher taking his items into account. Given he's the master of the skies, and has milennia of experience, he should take the advantages in mobility and experience as well. Along with this, Dragon Dance gives Rayquaza a significant boost in both power and speed every time it is used. Nomad will amp Rayquaza's AP throughout the match as well, as he'll be moving a lot. Extremespeed and Scary Face also give Rayquaza a solid edge in speed. Finally, Rayquaza seems to have a significant advantage in range too.