I am silly.
I saw "Bayo" in the first sentence and then saw "Bair" and my brain thought it was referring to Bayonetta.
I need coffee...
Whatever; what I said about Bayonetta still stands. And
@Megamang, in regarrds to Bayonetta's Dair, it likely has strong knockback on the final hit to replicate how the same move works in her home series; it drags aerial opponents down (regardless of where it hits I'll add;
be thankful for small mercies) and launches them away on the ground. Average combo finisher, and good for getting chip damage on opponents on the ground if you are finished with your aerial opponent. Not trying to defend it, but merely explaining why it's the case.
Speaking of which, I wonder if people who have actually played Bayonetta's games realise how similar but strangely different her moves are at the same time. Yes, ABK is a combo move in the air, but imagine if the Smash version was a multi hit that always ended with the opponent infront of you. Imagine if DABK was also a multi hit that dragged the opponent downwards (free pseudo-spikes bois). Imagine if Witch Twist could be done during a roll/dodge. Imagine if her dodges and Bat Within triggered Witch Time...
Smash Bayonetta still has more options than most/arguably all other characters, but she's incredibly weaker than her home series self. We should be thankful Sakurai didn't make a 1-to-1 copy of her and her move's original properties.
Then we'd all have been f*****.
Anyway, back to Smash...
Suppose I'll chip in on the actual Bair in question then; Corrin's Bair is indeed good. IIRC, you need to use it closer to the top of the short hop to make full use of the momentum shift. If it's done lower down the momentum shift won't help as much and can be punished. And as before if you space it near the base of the wings regardless, it should be punishable.
But the momentum shift itself can throw you off; you may think you could get a grab but because the momentum shift pushes him away you may need to use something else.; this is what makes it deceptive and a good move (that and it's overall kill power). It can also be confirmed into from a Dragon Fang Shot which KO's at a solid 90%-100% based on positioning near the ledge.
Also, in relation to something I saw earlier, Corrin's disadvantage isn't that bad. If Corrin's backed into a corner, it's not like he has a relatively quick, frame 8 instant move that can completely invalidate certain characters/forces a defensive option. Can be punished by a few characters but it can be used to reverse the pressure.
Nair is also surprisingly quick too; not Mario Nair (frame 3), but IIRC it's frame 6, which is kinda silly considering it's disjoint and hitbox coverage.