1st off we will talk about L cancel sex kick to jab. this is really fast, as are most characters aerial to jab combos (see fox, sheik, falco, falcon, peach, and even ganon) one reason is because when your move hits someones sheild, it stuns them for a while. this gives you time to throw out a jab just as they come out of their shield. this combo is very reliable and only runs into problems when the jab is crouch canceled. for instance falco could crouch cancel and then down tilt you or shine. still a good idea to jab after aerials tho because most of them will not be CC. and luigi is still fast enough to throw a move out before the opponent even when they cc.
2nd off, falco is too fast. if you are shield grabbing or doing any other move before falco does his shine, the falco you are playing is a tad bit slow. a perfect dair>shine cannot be prevented by luigi. you are better off wavedashing back and countering when they miss, or doing the same kind of thing with a dash attack.
as a side note, one possibility i have thought of (but dont think its very practicle, is you might be able to pull a hugs with luigi and up B out of your shield right after the dair or something like that. but the chances of you actually sweet spotting, added with the fact that falco really doesnt die from the up b, make it a pretty bad choice. Falco can be predictale with his dair to shine, id use that to your advantage. when you see ihm above you do a small to medium sized wavedash backwards, and punish him will he spams attacks at the ground.