Ummm.... DC, while you do make intelligent posts, you give the impression Kirby players don't know what to do when their air-camping is neutralized, which, as you stated, in this matchup it kind of is.
For one, you are completely right on your summary if all we do is air camp and Bair. This is a horrible idea vs ZSS, and we're better off approaching by shieldwalking and PSing until we get in.
Comboing will be ****ed up by DownB, but it's still possible. Gimping can also be ****ed by her DownB, but also potentially aided by it, since you can inhale her out of it if you predict it, and you can footstool her out of that.
Also, if you do a pummel break (only possible at the edge), it sets up perfectly for a gimp, since she really has very few options in that position, and all of them have a similar trajectory.
Most ZSS' will space with sideB and neutral B, and attempt to do midrange camping until they can start a combo, usually involving multiple Uairs. While these combos are very effective, we can avoid them by simply not getting hit by the 2-3 moves that can set them up.
Generally speaking, the way a ZSS player sets up combos will be either through a Dthrow, a Dtilt, or a Utilt. 2 of these require we be really close, and one requires she commit to a laggy grab. None of them are extremely hard to see coming. This doesn't negate them, since you will undoubtedly get comboed a few times, considering how well ZSS does that, but we shouldn't really be starting every stock getting comboed. In fact, I personally tend to do okay avoiding those Uair chains.
Yeah, her UpB clanks with our Dair most of the time, but for some reason, when they clank, our hitbox doesn't get canceled out like hers does, so we can still FF it and hit, whereas she won't be able to do anything about it. However, that's pretty situational, and you shouldn't be above ZSS anyway.
ZSS has better aerials and better air speed than us. Don't try to take this fight to the air.
Also, contrary to what some would like to believe, she is quite tough to gimp, and I wouldn't try to go too far away from the edge to gimp.
As for her armor pieces, try to get one and get rid of the others. You can then keep that one for a long time the same way she can: SH smash throw down, then regrab with an aerial (I use Uair).
ZSS' main problem is that she has no real response to excessive shielding, especially powershielding, due to her slow and fairly telegraphed grab. This makes getting in a lot simpler than it first appears. However, she does have tools for when you get in, so don't be too careless.
About her Dsmash:
It hurts... a lot... and it sets up for kills. That being said, it is also pretty telegraphed, and not all that fast... I mean, it isn't slow, but it's not incredibly fast either. However, the hitbox is bigger than it appears, and it does linger a bit, which makes it easy to follow up a Dsmash that hits a shield with another Dsmash. Because of this and it's ability to hit through the ground and ledges, while Dsmash is easy to see coming, it's not always easy to avoid, and it can be very hard to escape when getting Dsmashed on your shield.
Surprisingly, stone edgeguarding also works pretty well against ZSS, though it is risky, since if you miss, you can be punished hard, since ZSS can effectively gimp us as well when we recover from below (or if we need to use FC in general, or get too predictable.).
Also, you can duck her projectile unless it's fully charged, as well as her dash attack, which can force her to use SideB to reach you, which allows you a chance to powershield and approach her.
her aerials, while amazing, are also bad for approaches, especially on a character as short as Kirby.
Kirby's +
ZSS however is light , a fresh b-air will kill before 80%, f-smash far earlier.
With DI and DownB momentum canceling, there's no way a fresh Bair kills you at 80%. A Fsmash, MAYBE, but even then I doubt it would kill a good ZSS before 100-120%. I mean, I can't say I land too many Fsmashes at that percent on ZSS, but Bair killing at 80% sounds ridiculously wrong. Can someone test this?
Ugh... I've stopped and started this post so many times over the last 6 hours... I know I had other stuff to say, but I don't remember what anymore...
Not sure what I'd put this matchup at TBH. Somewhere between 50-50 and 40-60 IMO, though I wouldn't be TOO surprised if it were in Kirby's advantage... I don't know... It honestly depends on the style of ZSS and how gay the Kirby player is willing to be IMO (Also depends on the stage.).