The reason why I think the Sheik vs Kirby match up is worst then Sheik vs Meta knight has three main parts
1. Sheik can combo meta knight. Sheik has ftilt locks, dtilt locks and a good sum of moves that can lead into another hit like the whole force ground release thing. With Kirby we don't have any sort of combos, and no good strings I can think of.
2. Sheik chain can stops meta knight or it can be used to make him go around in a fashion that wont cause you to get punished. Kirby on the other hand has the perfect solution to the chain, fly over, and down B. Which I might add is a kill move, thus making the chain not as useful anymore at all.
3. Ninja aerial needle spamming kirby, is gay and very hard to punish even with dacus and counting his jumps.
Other then that if you manage to make sure kirby does not steal your needles or never gain control long enough to charge up you can force kirby to approach from the air. Unfortunately that's were kirby does his best. Everything you have either trades or is beaten out right and in a match were you are struggling just to land a few hits against a character who can kill you easier, faster, and can combo while you can't them trading isn't really worth it.
Something to note though is that Kirby up B cannot be used to force sheik to approach as with good timing you can hit kirby before he even lands also up B vanish baiting is easier to do since kirby doesn't have any sort of disjointed hit boxes and will be for the most part airborne.
On a personally note one thing that really pisses me off about kirby is that his grabs combo and his dash attack can't be side step while at the same time it has good priority. What the **** sakurai that's not just annoying, it's ****ing painful. On top of that Kirby fsmash out ranges rolls... and if it hits at the tip it sends people straight up b-b-broke.