I switched the words "Luigi" and "Marth" in your post, and it still made perfect sense. There, I got at you.
I play, almost every week, a marth who is at least top5 marths in the nation. He goes by xisin, and he HATES playing luigis. His rationale? One big mistake means a stock, it pisses him off. Also he hates bair. Why? because its a quick aerial with range, which isn't something you see very often outside of marth and MK.
The thing though is, he ***** my *** forever. In tournament I play DK on him, because its just a better move, and it makes the game an actual GAME every time.
A SMART marth, with a grasp on what options he has and is at least on your skill level, will beat you every time. I promise. Pinky swear.
Short hopped, retreating, double aerials from marth, are the bread and butter in this matchup. He uses them to FORCE you to do something you aren't comfortable doing. If you power shield the first fair/nair, he knows your options, and runs. Power shields are a good option, but they by no means imaginable "**** marth". When you're hanging on the ledge, 4 times out of 5, against a GOOD MARTH, you get hit.
Marth CAN BE gimped, but its a dumb idea, since one aerial at best puts you on the edge against an edgeguard. Marth does not gimp you, because tornado, if it hits, ****s him up hard. Neither option is useless, but neither option is a good idea (risk/reward), so nobody with a brain in this matchup actually does it.
Marth ****s luigi up, because luigi cannot approach and cannot cancel jabs without eating damage. Anyone in any matchup can bait a response and punish, therefore a better player can win anything. But when we're talking MATCHUPS, we're talking even playing field. On an even playing field, marth ****S LUIGI UP. Take up a kong.
If you doubt it, come down here and play xisin, I'll front you a money match. I have money to burn to educate luigis.
Edit, my edit was useless, so I'm editing it.
Kittens are adorable!