You realize that Xzard has to switch in to 4x SE stealth rock too? Like, that's not a Yzard only thing. Specifically this line confuses me; "You have to get the Mega Evo (which will mean surviving a hit on a switch-in and possible SR)", you mention it in the Yzard section but it is very true for both X and Y (Even if you meant to compare it to Ninetails, it's still true for Ninetales as well).
Charizard X can MEvo and then switch out and be safe from 50% even if SR's are out.
Char X and Char Y can both lead to avoid SR, and can both be set up to switch safely, but only Char X will be safe(er) to switch after all of that is already completed. That's why I can see Char X being the more popular choice for Rapid Spin teams. Not to mention Char X can use protect on the turn it Mega evolves and then switch in and out safely from then on if it chooses. Char Y would still have to worry of SR.
Also, what kind of buff did defog get?