By Inui logic I must be the best luigi! I'm glad this was brought up because the luigi boards don't know how much better I am than they are even though I still lose. =p Also praxis I'm picking up pika for some dumb matchups :D Like D3 once bojay starts infiniting me, and for MK :D
Also for the last time G/W isn't that bad and jab -> upB is super easy to land on him and it kills at like 2%.
If the G&W gets really smart and knows how to DI out of the combo, good luck.
You have to remember, Luigi's Jab combos are dependent on DI, so if he knows you want to Jab Up-B him at 41% whenever you get close, all he has to do is crouch and shield to escape it, or he can alternatively DI up and jump out of it.
It should be really obvious when Luigi wants to do it on G&W anyway, due to how limited his approach is in this matchup anyway, not to mention his limited defensive game in general. You seriously underestimate how limited Luigi's options are for getting close to G&W in the first place. It's not unlike getting shut down by Marth and having him Up-B out of your Jab combo when you do finally get close. =/
G&W is also an extremely difficult character to powershield. You won't be powershielding his Smashes on reaction if he knows that he has something like a 3 frame release on his D-smash and a 2 frame release on Up-smash, and even if his startup is just average, most of his attacks do come out before reaction time, and he has great mobility and multihit options.
The only good news is that most G&W players suck and don't actually know how to use the character correctly, and UTD Zac's matchup knowledge is apparently all against S/A tiers and Yoshi basically.