I think you forgot Extreme Speed is 156 base power Flying move (with STAB) which is stronger than a STAB Return. Also with +6 attack, it will do lots of damage, I personally see a 1HKO on all non-Unware or heavily defensive types that resist it such as Mega Aggron.
Scizor, being Bug and Steel is neutral to Extreme Speed, so even without a belly drum, it will take even more than it would from its STAB Diamond Storm (150 with STAB).
Also Xerneus is commonly used with Pixelate, and Kyurem Black or White is also common in general with Refrigerate. So to say Extreme Speed won't be doing much after a Belly Drum is misleading. And Kyurem-Black or White has to ensure it doesn't switch into Diamond Storm in the first place. Aerodactyl can survive Xerneus Fake-outs easily and then go first the following turnfor the 1HKO with extreme speed, but needs to watch out for Fake-out Refrigerate Fake out at 50% HP after Belly Drum. With 405x4=1620 Attack, I think a neutral 156 base power Extreme Speed will do a lot.
I do agree Bullet Punch on Scizor is less common, but I was just using a priority move that was Super Effective besides Refrigerate Fake-out or Extreme Speed.
As for Yvetyl and Rayquaza, I chose Aero for the speedy Spore to get the free turn to Belly Drum and maintain momentum in going first with Extreme Speed. Obviously it can use regular priority moves like Diamond Storm for its +Def effect and for good coverage (I.e. A rock-type switch in like Regirock or Mega Tyranitar coming in on Extreme Speed). I'm sure the better coverage from thousand arrows and it's ability to hit flying types and levitators can serve Aerodactyl even better to handle Dual type Flying types like Ho-oh, or Levitate Heatran, in addition to the Steel, Fire, Electric, Poison, and Rock types hard.
Also I don't want my Aerilate Pokemon weak to Pixelate Xerneus ' fake out, as they are also already weak to refrigerate fake out