Maybe I missed something in the link you posed but what I read was about shielding right after the PS window and not the PS itself? Even then, would kirby still lose the frame advantage? Dsmash would hit at frame 20, and ZSS first active frame is 42. So that means Kirby would have to be locked in shield for 22 frames for ZSS to have the advantage correct? So lets say you hit kirby on frame 4, the earliest you cant in shield lock. That means Kirby gets 3 frames of shields stun, plus the remaining 7 from shield lock, plus 7 frames for shield drop, plust 8 frames hit lag. 25 frames correct? So a 3 frame advantage if kirby chooses to drop shield though. As per the your link though, if Kirby chooses jumpcancel/roll/shield grab, he can act at the same time he normally would and still maintain frame advantage. Did I miss something?
Anyways, apologies to Trifroze. I got a bit snarky there.