Like?
Roll = Get hit
Spotdodge = Get hit
Jump = Get hit
Double jump = Get hit
Run to the middle of the stage = Get hit
Retreat back tot he ledge = Back where you started..
Can your opponent react to each one of those options without fail while not sacrificing ability to react to the others?
Many things in smash require an amount of guessing, if you're telling me that peach/marth/armada players has the ability to react to split second decisions accurately 100% of the time then I don't know what hope the rest of us who lack super human reaction speed have.
I'm trying to imagine how peach can cover all of sheiks options when she's on the edge.
Jump - pretty slow, easy to react to
Roll - if predicted at low %'s can get you throw back off stage, high %'s dsmash might cover this quite nicely
Get up - pre 100% fairly hard to react to unless predicted, post 100% if you know the animation fairly easy to react to and punish
WD on - you have quite a few options out of this, attack, spot dodge, jump, roll, I can't possibly believe that you can't change things up and still not be able to get back onto the stage.
I can't see peach standing in wait and reacting to every one of these options and the ones I forgot to mention.
Granted I don't have the level of experience you do against the level of opponents you do but I do fight marths on a regular basis and have never felt it impossible to get back onto the ledge once I grabbed it, and I can't invincibly wavedash as samus.
I'm sorry if you've run through all these options and have come to the same conclusion, but while I believe that yes getting back onto the stage is a chore, it's not impossible, and shouldn't be as easy to punish as I've understood you are trying to make it seem.