bair is the only move in the air kirby has over us, and if they use it too much, the y lose that kill move. plus bair walls dont do well to gimp sonic. we know about their recovery, an dour tilts are overall better too. uptilt is kirby's best one , but OOs usually.
in the end kirby has to play a lot resevered in order to beat sonic. they have to wait and guess your actions while fishing for lots of grabs since thier combos get stopped by spring early. kirby has to play very defensive to get a chance to rack damage on sonic, and he can't force a bad approach since he has no projectile, so spins and th cancels really help cover intentions and force his hand rather than the other way around.
Teere is not real set up for kirby's kill moves either. Kirby has to use multiple mindgames in order to kill sonic, IMO, seeing as Sonic has the higher potential for mindgames and can adjust spacing better, as well as being able to survive longer, sonic can out last kirby longer.
but since Sonic has even less kill moves thatn kirby and has a hard time gimping kirby as well, he can have trouble if he gets too careless. even then, since both have to rely on thier mindagmes to land thier kill moves usually, sonic's higher potential to do so gives him teh edge.
this is in sonic's favor. 55:45