If all you ever do is hit the shield button based on reaction to an animation you'll never perfect shield anything other than a projectile. You perfect shield 6 frame attacks the same way you parry any attack in any fighting game. An approaching ZSS sets up easy reads for a ducking kirby with simple options that cover everything ZSS throws at you.
Right, well ZSS can take all of her mobility and run around showing off all of her tools. Crouching Kirby doesn't care. Mobility doesn't mean anything to a target you can't pressure.
Proper spacing for kirby is with his foot in your face, safely above your nair.
None of this changes the fact that ZSS retains more options relative to Kirby whether it's a crouching scenario or not. Kirby's only options while crouching that pose a threat to ZSS are well-used defensive options into punishes. Kirby puts out no offensive pressure while crouching unless you go right up into his face, and clicking shield in anticipation of an attack can be baited from Kirby just like any other time. "ZSS can take all her mobility and run around" is actually a perfect example to emphasize how badly this sort of "crouch camping" works. You can simply keep dashing towards Kirby over and over and eventually make it all the way and either:
1. attack out of a dash with jc usmash, up b or pivot ftilt and:
a) hit him
b) get shielded and punished
2. put up shield in front of him to bait out an option and:
a) punish a move he threw out
b) up b or usmash out of shield if he does nothing
c) get grabbed
3. spotdodge or roll to bait out an option and:
a) evade a grab attempt and punish
b) evade an attack and punish
c) get punished for your option
4. fox trot into midrange to bait out an option and:
a) punish
b) hit him with dtilt, dsmash, jc usmash or side b by surprise
c) throw out side b or dsmash and do shield damage
d) throw out dtilt or jc usmash and get shielded and punished
This simple running around already puts you in a favorable scenario or forces Kirby to do something other than crouch because him being stationary makes him the player who has to guess one out of your several options. In addition you have tomahawks into ground options or dair while also partially covering Kirby's option of jumping out of his crouch, probably other things too that I couldn't come up with off the top of my head.
Also, above ZSS' nair is generally a place where you shouldn't be because you don't want that A button to be C-stick up into itself over and over instead. If Kirby's optimal spacing involves aerially challenging a character with more range and fast juggling aerials from an angle where Kirby can get hit by them, neutral sounds dangerous for him to say the least.
Anyway, I don't think this conversation serves purpose any longer as you've ignored most of the points I've made and stated several hard data related things incorrectly, all of which make this very unconstructive.