yeah luigi’s approach game is his weak point (which is why i think mario is better overall)
luigi’s movement is floaty and his run speed is actually good but still outsped by sheik.
sheik’s main strength in the matchup is needles to rack up free damage from afar and essentially negate luigi’s fireball game, as well as her superior movement to dictate the distance between them.
if sheik starts a juggle on luigi, yes luigi nair is good as a fast get off me move that puts sheik above him. however, if it is baited, it is a free punish into the same situation. this is pretty much the case for the rest of his landing options as well, except maybe airdodge. tornado is pretty easy to punish if baited as well.
luigi’s main KO move, usmash, is pretty limited against sheik who falls fast enough to make it hard for luigi to get in a landing-trap position when considering DI. instead, luigi will often have to rely on very high percentage Bairs/Bthrows. while these are already somewhat difficult to land on a sheik who doesn’t want to get hit, the high percentage she needs to be at makes it worse. I’m not too certain about luigi’s edgeguard game, but it is a bit dangerous to do vs Sheik’s high priority up b. at the same time, it may be his only real chance to take stocks at lower percents.
yes sheik can get hit at close range and that’s bad news (often a lot of damage racked up by luigi), but the struggle to KO her somewhat mitigates the threat of the damaging strings luigi can do. and of course, the neutral game domination by sheik is the biggest issue.
sheik’s ability to edgeguard luigi is extra bad news for luigi, as her weak KO power is somewhat mitigated by how much of an advantage she has when putting luigi off the stage. once luigi has exhausted his down b and double jump, he is in big trouble.
while he can definitely tech any stagespike attempt vs when luigi side b’s into the stage, it’s still a lot of time for sheik to go for it (and you cannot walltech for a small period of time after pressing Shield, so it even becomes a small timing mixup)
right now i think it is 7-3 sheik over luigi. VERY bad.