Jab doesn't really have great priority, per se. It's just a fast move that does average ground move damage. IIRC, there's a certain damage percentage range (which is relatively large) where, if two moves hit, they simply clash. Where "priority" typically comes into play, is with disjointed hitboxes. If Falcon hits a disjointed hitbox that does similar damage, chances are, the disjointed move is going to hit a Falcon hurtbox, while Falcon's move is going to hit nothing but a hitbox (which isn't good enough, so he loses and gets hits). I believe it works something like that (?).
People think jab is good because we're usually in our opponents face when using it, so they're usually using fast ground moves, which are less often disjointed. Also, one might think it has better priority because it's so fast, when really, it's just hitting your opponent before a hitbox comes out for their attack.
Falcon Punch or whatever clashing with a weegee fireball is because it's a projectile. I think you need some kind of other properties to go through projectiles (forget what they were, I know the Balanced Brawl project added it to Ganon's down-b so that, the first time he uses it with no decay, he goes through projectiles). It might just be an absurd amount of initial damage. Not sure though.
Falcon's "priority" just sucks because he has no disjoint, and 99% of the time, if he clashes with a disjoint hitbox of any kind, he loses. And there are tons of characters with many disjointed moves. Falcon just has utilt (which is indeed awesome).
Although, utilt is still hard to hit Wario's bite with. I play a Wario main pretty often, and it has to be spaced very well. However I do believe it is the only move in his entire moveset that can hit Wario while doing bite.
