This matchup is not that bad at all, I would put it absolutely no worse than -2 for Lucas. I would probably put it at only -1, actually.
The problem is that there are very few good Lucas players, and a less knowledgeable Lucas who doesn't space properly and bait/punish is just going to get grabbed over and over again, which make make it seem bad, but it's really not imo.
The most important thing though is Lucas's aerial mobility, he can literally run circles around DeDeDe and make approaching or ever getting a grab incredibly difficult.
The same can be said about Wario. Just because Lucas has air mobility, doesn't mean that he can just go around and ****ting on people. That's like saying he can do the same thing against Snake. Jumping around doesn't help in this MU, it gets you b-aired.
Lucas can space DeDeDe with retreating f-air, pk-fire, etc. He can wear down DeDeDe's shield fairly safely with well spaced aerials such as n-air and more retreating pk-fires. One of the things that I think Lucas does really well against DeDeDe is bait grabs and then punish. Lucas has very good air traction so he can bob and weave around DeDeDe with relative ease while baiting and punishing.
Lucas can "space" Dedede, but he's not going to poke anytime soon. PK Fire should almost always be powershielded. And it's still hard to land on an aerial D3 because his fast fall is so fast, he can usually FF Airdodge past it. F-air is okay, until you realize it won't be poking and you're doing nothing but backing yourself up in the corner against him.
"Bait grabs and punish" - ermmm D3 isn't playing the MU well enough if he's being baited hard. This sort of means that the D3 isn't playing top level, where he should know the conditions to grab Lucas. Air traction? It honestly seems like you're just being flat out outplayed by FAE the way you describe this MU.
Lucas's ridiculously fast Jab and mixups from it (jabs > retreating nair especially) also give DeDeDe trouble close range, since all DeDeDe has at close range is grab. He's not Falco, he can't jab. ALL he has is grab. That's it.
Lucas' Jab is cool. at first. Then SDI. If the D3 SDI's the jab, he puts Lucas in a terrible position. If you anticipate the SDI, you just realized you get three damage on D3 and put yourself in a bad situation CC against him.
Lucas also edge guards DeDeDe fairly well because he can safely PK thunder to eat DeDeDe's jumps and force an up-b, then punish with [really strong lucas KO move of choice] or an aerial.
[insert how D3 can grab the ledge, making landing the KO move near impossible out of his recovery]
You should also be DIing the PK Thunder so you get hit to the stage. It's extremely easy to influence where you get hit from PK Thunder.
DeDeDe really doesn't gimp Lucas very easily either. While it's obviously a concern, lucas can use zap-jump or psimagnet momentum and his up-b to recovery pretty easily so long as he doesn't make any incredibly poor decisions.
No one really "gimps" Lucas except for MK and a few rare instances. Everyone is just able to get heavy damage on Lucas off stage. Which D3 can do great with b-air. Then he gets Lucas on the ledge, where he can ledge trap him really well. Lucas is pretty much stuck in a corner once he's ledge trapped where he takes a crap load of damage.
DeDeDe is fat and that can make him live through things and stale some of Lucas's moves, in addition to the obvious issues he presents with grabs. Getting CG'd as Lucas really isn't as bad as it seems for him though, and actually grabbing a knowledgeable Lucas is pretty damn hard.
It sort of is bad for Lucas, especially with the discovery of SCSG making the CG even longer. Then Lucas is forced to the ledge where, he has even more trouble getting out.
