Some of what I'm hearing about G&W is kinda odd to me; I kinda feel like people maybe didn't understand him all that well in Brawl. I was about to give a huge Brawl G&W clinic, but this is the 4 topic so going into depth about how he worked in Brawl wouldn't help anyone (I will point out to Shaya that his usmash and dsmash already did those things and to my buddy Thinkaman that it wasn't the MKs that kept me down it was the Snakes).
So, to keep it 4-centric, let's talk about what G&W's core gameplan actually is. G&W has horrible "boxing" potential as his moves don't really flow into each other well at all and are really slow/unsafe to use at point blank, but he has a ton of really big disjoints so you have to look at him like he has a sword just like Marth except unlike Marth his sword is a bunch of random objects and not a single blade. Generally speaking his aerials are a lot better than his ground moves, and he also has very high aerial mobility overall (it's weird but averages out to very good!). This makes him the best air to air character in the game. Even in 4, I would not be confident air to airing G&W with anyone who is not also G&W except maybe the super unconventional Villager stuff and Shulk with that wall of nair who at least needs to stay low to the ground while G&W is more than happy to fight way up there. He has pretty significant holes in his gameplan otherwise. His aerials pretty much beat everything, but they don't flow together. In fact, none of his moves do which means he is one of the most rigid characters in terms of playstyle. His entire gameplan is to use his good movement to set up spacing for his good, disjointed pokes which are mostly but not quite entirely aerials. If things begin to go wrong, Fire is a good panic button for a lot of reasons. Keep poking and chipping away by relying on the best spacing you can muster, avoid ever playing cqc since you pretty much always lose at that (somewhat less hard now thanks to rapid jab working and dthrow having a pay-off but it's still not good overall), use your priority to lock down fast characters and your movement to control the match pace against other disjoints, and always have an eye open for ambiguous situations in which you can land a power move since the risk-reward tends to be pretty good and you are in this for the long haul.
This just seems a lot harder with bair being a lot less safe and less rewarding all at once, the power move pay-off is considerably lower now, and you don't survive as long either. G&W is a very rigid character so I'm not really seeing the alternative. He's never going to have a fast paced, mix-up based offense. He just lacks the tools for it in a huge way. He'll always have to play slowly and rely on patient spacing to get his edge, and while I don't think he's a ruined character (he can still do it okay, just not as well as he used to), it's an already hard road to victory that seems even harder now. His "jank factor" is basically the natural way his moveset does unusually well in an early metagame. In an early metagame, many players lack patience and play faster than their characters can handle, and many players lack tight control over their characters. Both of these things result in players just running into the wall that is G&W's priority, but that will change with time as the strong offenses and defenses both from other players get far more precise and disciplined.
I do think he has one extra avenue here that mostly stems from how both of his new up+B options give him a super crazy vertical game and Short Order Chef is actually a legitimate projectile; I could imagine playing what is basically projectile run-away to force people to play the up-down game more and using his Fire variants a lot to win at that. That relies on the custom move cause emerging victorious of course, and even with that, I'm not entirely sold that's a top tier gameplan so much as a mid tier one.
I'm not sold on G&W having such good MUs versus top characters here. He probably does okay against Diddy and Sheik, (definitely not sold on him winning those but they are probably pretty fair to him) but on the other side, I'm seeing likely big negatives for him against Lucario and Yoshi which could be a big problem going forward and while a lot of people don't believe in him for some reason I would be very, very scared to fight Shulk with G&W and would be very concerned with fighting any power character honestly. If I wanted to go anti-metagame at this point, I'd be looking into Peach and Jigglypuff a whole lot harder than I'd be looking into G&W; they seem to offer a lot of the same positives in terms of the stuff thye can challenge with less downside from where I'm sitting.
In terms of the engine changes and pros-cons other than weight for G&W to answer a specific question, yes he can challenge landings really well with his disjoints but the downside is that he doesn't exactly inspire his foes to jump at him very much (most characters do better just keeping their feet on the ground against G&W, though Short Order Chef could help him use this more for sure). G&W still has an awful "combo" game while other characters can now possibly string hits against him. G&W really just hates everything about the ledge changes; his ledge game was super good in Brawl and while still probably decent here is definitely way less consequential and way less powerful. In general honestly most characters jump less than they used to, and since G&W's best areas are air to air and even out of shield anti-air with Fire that's a bummer for him. The upside is that the average recovery being worse makes his good gimp game relatively more important which may be the area strong G&Ws have to focus very hard in 4, but even that's bittersweet as his own recovery is very much on the list of recoveries that are a lot worse.
Sorry to post so much about G&W; that's pretty much the long version of why I'm not sold. If I saw a very strong G&W playing offline do stuff fundamentally different than what he could do in Brawl and see success I could be persuaded I've missed the point on 4 G&W for sure (I always consider it highly credible that anyone, including me, has missed the point of characters in a game this young), but for now I feel pretty great about my decision to drop him as a main.