It all comes down to moveset design and what they could offer to diversify the roster. It isn't really about the aesthetics but rather the function. In this case, let's go back to WL and WW Wario. What can WL offer? A shoulder bash, a buttstomp and throwing enemies. The latter is a bit difficult to implement, but the former two are pretty standard fighting moves. Having them be designed to have large roles would be underwhelming. WL Wario is a pretty straightforward "beat up what's in the way" character archetype, compared to the zaniness and laziness of Warioware Wario. WW Wario may NOT do much in terms of actual fighting, but imagining him fight is an easy task that's open to be creative. Warioware Wario in Brawl kinda fills the acrobatic fat style that Smash doesn't have (see: Rufus in Street Fighter, Bob in Tekken). Pull in moves from various Warioware stuff, and you got yourself a largely unique utility based fighter that's unheard of in Smash. (Besides Snake in a way) Project M Wario in comparison is pretty much another Jigglypuff.
I box, so it's very easy for me to see why Lil Mac can work. It's not that he doesn't looks generic, I can understand thinking that (though I think he's too...spiced up in Smash. Exaggerated animations and all giving him a bad form which the boxer in me does NOT like lol), but he definitely brings something new to the table. I was actually thinking he'd be a pressure based fighter who has a huge advantage if you're on the defense or a stance based fighter, but Sakuri went with being a monster ground fighter who is weak on air which I respect because it goes with the whole basic idea of how balancing your feet on the ground and footwork in general is one of the most important thing in boxing. I'm drawing blank for Pac Man though, no matter how unique he'll LOOK, I feel like he'll PLAY like a more standard fighter. I do want Pac Man in, so don't get me wrong, and in fact I'm more excited to see what Sakurai does to him because of that.