Couldn't ledgehop uair to fsmash work?
if the marth player switches to roy, then yes.
ZSS is probably going to be holding towards the middle of the stage. DI isnt really going to allow anything more than a sourspot, and likely going the other way, not back offstage. uair > fsmash really only seems to often happen on space animals, or with platforms while rising up to properly control the difference in height. doubt youll see uair > tipper too often
you can rattle off every single possible marth punish that could "possibly" work, but when it comes down to it, too many of these punishes are too DI dependent, spacing dependent, and require too much of a read on both of those things. thats why roy is such a better tether punisher, because his sweetspots dont require incredible spacing. roys punish game is a 50/50 guess on which way shes gonna DI the dair. fsmash/bair are a threat if she DIs away after the dair, and if she survival DIs instead, then shes getting ken comboed. if she tries to smash DI away on the dair, a simple ledge hop fsmash might take care of things. if you want to switch it up, you could simply ledge dash > dtilt/fsmash. another 50/50 DI mixup, both are heavily rewarding.
fox doesnt even need a good read. ledge dash > charged up smash on reaction should suffice. you could even bair to cover drift away, then upsmash to cover the landing.
falcon can outright reverse knee you, or if he fears the amsah tech, then he could just dair > knee you. now falcons neutral is more threatening to ZSS, and his punish game on her is even arguable better than marths (especially considering links to kills). EVEN with that, there are stages that ZSS beats falcon on. its hard to use one MU in general as a reason that another MU is bad, but in this case, thats two very integral areas of play to consider. when weighed next to each other, marth doesnt look quite as appealing to be the one to deal with ZSS.
these are few examples of how other characters deal with her. there are many more I could go into, but since they are relatively common characters, and provide clean examples of certain attributes, I feel them to be a good example. when you use these characters as a base to see what kinds of things can beat ZSS in certain situations, marth doesnt have them.
1.)lacks relevant kills from conversions (fox, falcon, and roy all have great conversions to get consistent kills).
2.)lacks ability to provide a safe answer to her projectile (falcons/fox's nair are far superior to deal with it, and theyre more mobile characters)
3.)lacks safer conversions from neutral (compare marths grab to roys safer, and longer ranged dtilt)
4.)lacks ability to cleanly edge guard her without too much difficulty (there are too many reads he needs to make on her burst mobility, multiple jumps, projectile, and wall jumps)
5.)lacks ability to get a consistent kill conversion from punishing a tether hop
now even with this, I have already previously explained why i think marth can go around even with her on smaller stages, but heres a more organized interpretation of it: Point 3 is mitigated due to the increased ability of things like fsmash, tilts, and his grab to cover space on the stage; point 2 is also mitigated since her projectile isnt as safe when the stage space is crammed; point 1 is mitigated as a result of 2 and 3 directly being mitigated by stage size; the nature of ZSSs ability to recover with walls and use platform layouts to her advantage (both for neutral, and for escaping juggles) depends on if its GHZ,FoD, WW, etc, but point 4 still remains an area where marth wont really excel; point 5 remains in tact.
