ness and link can get CGed til like... 90%. you can cg pikachu until like 90% and finish it off with a usmash. Not 100% on that since it's been a long long time since I played a Pika (and he wasn't even good), but meh.
BTW, I played a very good Kirby for about 3 hours last night, and while Sheik has a big advantage, 90% is likely overstating it.
At low %s, a grab is 45ish percent on him. The best way to get in a grab is wait for him to do an aerial, space well, needle him before he hits the ground when he's done / finishing his aerial, and grab. Hit once, dthrow. He'll DI away. Chain grab him. Hit once, dthrow. He'll likely DI in. Usmash. If he DIs away, chain grab again.
At low percentages Kirby is destroyed by grab --> cg ---> usmash or nair or fair. If they mess up the DI on the usmash when he's in the 20s, you can follow up with a uair.
Kirby won't die to a dthrow uair until about 90%, assuming they DI very well.
Edge guarding kirby is more difficult than you implied, because a Kirby capitalizes very well off an inexperienced Sheik's edge guarding. But once you have it down, it's ridiculously easy / broken. Kirby likes to come in for below, but low enough where jumping down from the ledge and bair won't usually work. Sometimes it's best to not necessarily wait until he's up bing to nair him, but the jump or two jumps before he has to up b.
You didn't mention it buy dair owns Kirby so badly. It goes through all his moves but utilt, uair, and a well-spaced bair. And when it hits, it's an easy uair, which is obviously the easiest way to kill Kirby.
Kirby's favorite approach are usually perfectly spaced fairs, whichi you really can't do anything about since it outprioritizes everything. Instead, try to space his attack off well so you can counterattack -- dsmash works really well and I find myself dsmashing a lot v Kirby because there's not much he can do about it. Sheik's CC owns Kirby quite hard. If Kirby is even slightly off in his bair or fair angles, dsmash hits him out of it.
Kirby is also horrendous at stopping needles, so I like to charge needles, throw them when he lands, which usually hit since his aerial manueverability is garbage, and then do it some more. 18% means a ton to Kirby, since you'll be killing him around 100 or earlier (stage dependant).
Usmash is also godly if you can get his tech right or something to that extent. That will kill him around 70%.
I know few people are going to play a good Kirby, but when I did I was confused, so I may as well add in my experience.
EDIT: I'd like a more in-depth Mario if you care enough. MArio's so much faster than Doc that I'm trying to play him like DOc and I'm off-balanced. If I played him more often I obviously could adjust, but just saying -- I think they're pretty different.