If Ness and Lucas play the same against Mr. Game & Watch, those would have to be some pretty awful players, probably the Ness players playing badly (Ness's forward aerial changes everything; it's so good!). Really, Ness and Lucas are very, very different. I don't want to get in a war with anyone over how good Ness and Lucas are so I'll try to focus mostly on what they do against Mr. Game & Watch.
Anyway, Lucas is pretty easy to beat, but he's not ridiculously easy or anything. Lucas has a VERY good down aerial which isn't especially effective against Mr. Game & Watch but is a big thing to look out for regardless. Lucas will use it to rack huge damage if you leave yourself open to it. Moving past Lucas's ace in the hole move, Lucas is mostly going to focus on answering what you do and being careful while trying to exploit his general high level of power. Lucas has a pretty solid pivot grab that he can kinda camp with to make spacing him tricky, and his shieldgrab with the long range tether makes him more difficult than average to shield pressure. His tilts are all pretty decent, and you always have to be careful of that fsmash which kills low. His down smash is something that's interesting if nothing else. It's not actually that good, but it hits in a really odd way that forces you to alter what you do defensively in front of him a bit to accommodate. Lucas can also use his nair kinda like Mr. Game & Watch uses his. It's a lot worse, but it's kinda fast and hurts if he snares you in it.
A lot of Lucas players make him look bad by focusing on bad offensive moves like up smash, Pk Fire, and Pk Freeze (all of Lucas's specials are bad except for recovery and energy projectile absorption actually). The general way Lucas goes about it, in short, is camping with his grab and safe jab/tilts while punishing with his strong fsmash and using the times he happens to be in the air to try to snare you with a few high damage moves. The fact that Mr. Game & Watch has a lot of flat out superior tools to prevent Lucas from taking the battle to the air really does limit him a lot (Lucas at least has pretty good aerial mobility so he can get down when the situation calls for it), but Lucas isn't particularly easier to beat than most other low tiers. All around he's probably 65/35*.
*HOWEVER, I should point out that it would be a total joke to ever give Lucas a better score than Ness; Ness is simply a radically bigger threat than Lucas could ever be. Lucas is indeed very different from Ness, but a lot of the reason is that in a lot of moveslots Ness either has a radically superior version of the move (uair, bair, bthrow, Pk Thunder) or a move really fundamentally different that's actually functional while Lucas's move in that place is either awful or just really limited (usmash, dash grab, fair). It really just lets Ness do a lot more to Mr. Game & Watch than Lucas can, especially in terms of being able to actually apply pressure instead of having to play mostly reactively. Lucas has a few things that are better, but they don't save him from being "the bad Ness" any more than Fox's stuff like that saves him from being "the bad Falco" (having a tether grab is really the only advantage Lucas has that is a big help against Mr. Game & Watch, though his ridiculously good recovery is nice too). Really, Ness should be 60-40, but since this isn't about Ness, I don't really want to lay out the case now. I'm not sure what I suggest putting in for Lucas's score actually, but whatever it is, it definitely needs to be a worse number than Ness has.