KMD, Fox and Falco (in Melee) vehemently disagree. Their aerials were some of the most prioritized attacks in the game.
Falco’s Dair, for instance, has so much raw priority, most people can, at best, trade hits. The only real way to go through it is with Disjointed Hitboxes. This is because parts of Falco’s legs are actually invincible during the Dair. Fox’s Dair has a large hitbox and a decent priority as well, but not as much as Falco’s.
Their Nairs and Bairs have a lot priority as well. Ever seen them randomly hit people with Fox and Falco not trading hits when it looks like they should? Priority. Upair as Fox (1st hit) has ridiculous priority. Falco’s has less so.
Dsmash with Falco has his legs invincible during charging. Not sure about when he’s actually smashing (I don’t actually play as Fox or Falco). Some of Fox’s and Falco’s smashes have some of the games’ highest priority, like their Fsmashes and Fox’s Usmash.
In the game, very few games have actual True Priority. True Priority is what happens when two ground attacks come out at the same time. In most cases, the attacks would clank and stop. But not with True Priority attacks! They’ll cancel out the other attacks (if they’re too low on priority) and actually continue and hit the opponent.
That’s right, if you, for example, jab as Peach against Fox’s and Falco’s smashes, Peach’s jab will clank and stop while their smashes still come out and hit her. This holds true for a lot of other lower-prioritized attacks vs. Fox’s and Falco’s smashes as well.
Fox and Falco are priority powerhouses. The only attacks they have that have low priority are Up + B (more priority for Falco) and Over B (crap priority for both as their hitboxes are actually behind Fox and Falco, meaning you can hit them way before their hitboxes are anywhere near you).
Peach and Sheik are priority powerhouses as well. Peach’s Nair, Dashattack, jab, F-tilt, Bair, Dsmash, among other things. Pretty much all of Sheik’s aerials except Dair and to an extent Uair (which has medium priority) + all of her tilts, Dsmash.
Regarding Sonic’s Up B: You cannot meteor cancel indefinitely because of how it works now. At certain %s, there’ll be nothing for Sonic to do but die after getting meteor smashed, even if he meteor cancels since he won’t make it back.
And there’s also the much more obvious options: A simple aerial. Either try to go for a stage-spike (unreliable) or do a Nair/Fair/Bair so that he’ll fly off from the stage again and keep edgeguarding. Because his recovery is almost entirely vertical, he’ll eventually be too far away to make it back.
It’s not the crappiest recovery in the game, but it’s not very good, either.