if you can't win without using the same tactic over and over again, perhaps you're the one that needs to get good
Uh not really, I've tried many methods of edgeguarding and the jab is by far the strongest move to edgeguard because it is Marth's longest range attack and knocks people back farther than any of his other attacks, so it's his best method of keeping people from recovering once you throw them off.
If jabbing at ledge was an undefeatable strat it would be how every Marth edgeguards every character
Not being able to get around a defeatable strategy is a marked sign of scrubness. Using a strategy that others cannot beat is at worst cruel opportunism. Has nothing to do with his skill.
Edgeguarding is certainly defeatable, I can't do it perfectly 100% of the time, not even Leffen can edgeguard perfectly 100% of the time. If I forget up timing, they have an easy opportunity to get back on the stage, but they're just bad and burn their recovery before they see me mess up and then rage.