Dude. Those don't even compare. Moody relies squarely on luck. Mega Rayquaza was broken as fuck. For starters, the latter was not bound by the normal rules for Mega Evolution; unlike other megas, it only needed to know a certain move, this being Dragon Ascent. This means it was free to hold another item and take its already obscene power to another level or boost its survivability. Because of all this, peeps had to run gimmicky sets just to beat it. That being said, they are both uncompetitive, albeit for different reasons.well, then you are telling me that the goofy aah ability is as uncompetitive as mega raykuaza?
Dondozo lacks recovery except the very exploitable Rest, which is already problematic, but Rest fails completely when Electric Terrain is active. That's an issue when Miraidon is the best mon in the tier. Also, what are you gonna give up for Haze (putting aside the fact that if I have to actually consider running Haze on an Unaware mon, something is wrong)? One of the Moody abusers having a move that is super effective vs it is also something to consider (also, the other abuser has Leech Seed)...like i see some checks, haze dondozo, skeledirge, any roar user, taunt users.
252 SpA Glalie Freeze-Dry vs. 252 HP / 4 SpD Dondozo: 236-278 (46.8 - 55.1%) -- 14.1% chance to 2HKO after Leftovers recovery
That's already not looking good...
Roar works... unless you happen to be stuck with Scovillain or Glalie as the last mon standing. Well, other than the part where they get a chance to hit and possibly KO you before that, as Roar and Whirlwind are forced to go last.
TL;DR Moody can only really be consistently dealt with by going out of your way to counter it (and getting lucky)... which puts you at a disadvantage against the rest of the tier.