if by higher tier you mean high and top tier, then yeah luigi doesnt combo as well as them, nobody does.
If by higher tier you man samus, and then doc down to luigi (which i think 6 characters), then luigi actually combos BETTER than them.
Heck, you can throw capfal in there too, because capfal has to come to luigi, and luigi can combo the mess outta FFers and reg. weights with d.smash, u.tilt, and n.air.
Yeah his recovery blows (because the heart of his recovery is random), and sure his approaches arent specifically hot (he's got some options), but a good luigi is hard to get away from. And you have to get away from luigi or you get the **** kicked outta you.