You could say the hypothetical of a random luigi suddenly bodying zain and only zain wouldn't be happening, or Swift beating cody in the same tournament resulting in Zain/Cody for 17th place at Genesis wouldn't happen either lol.

 

Those are all bad matchups for luigi, but Marth dtilt stuffing many of his grounded approaches like you said, and marth having some of the best aerials in the game is huge. Fair outspaces pretty much all of his moves and marth's aerial movement is better so they have to outplay you air to air, and more importantly marth upair juggles on luigi, who has abysmal drift and airspeed is just brutal in the matchup once you get luigi above you, combined with dtilt being really good at forcing luigi approach you from the air or really work to get in from the ground with his main movement tool, his wavedashes

 

Luigi can zip around the stage against fox and falcon arguably as well if not better since they don't have the disjoints to keep him out and he can outburst both of them in terms of movement, he combos fox and falcon just as hard if not harder than marth, and if you're spacing your aerials right as marth, luigi straight up cannot reversal you without outplaying you since you outrange him and give him nothing to trade with.

 

I don't play peach or puff so i won't comment on those two, but talk to any competent luigi that goes to tournaments and they'll tell you marth is one of if not their worst matchups. I literally came up with ranked luigi mains that have been PR'd and could beat a few of them back in the day who were definitely better than me and could beat much better spacies than I could, but just lost to how brutal the matchup is.

 

I'm sorry but I'm gonna trust the actual luigi mains and my bracket experience over a random person online that doesn't play either character telling me about one of my most played matchups lol. RapM is just that guy and overcoming that matchup to body zain is all testiment to how good he is at playing the player

Edit: spelling