G&W infuriates me, not because he's a bad match-up or anything, but his hitboxes are just so weird that he's hard to beat out.
Don't get grabbed. It can set you up for some pretty early cheese kills if they draw a 9 hammer, and his throws are great for setting up for follow ups. Bacon is pretty annoying, it basically creates a space directly in front of and slightly above G&W that stops Dedede from properly approaching.
Mainly we want to abuse our disjoints in this match. Ftilt is a godsend because it out ranges pretty much everything he does and allows us to poke at him from a safe distance. Once he's in the air, we just want to juggle him. He's super light, so he'll die early from a well placed bair.
Never drop in from above unless you want to get hit by the diving helmet. That usmash has armor properties that stop us from safely landing on it. Besides that, he can keep us floating up in the air with his uair, it's not a pleasant spot to be in.
I'm pretty sure Dedede beats Gdubs solidly, we just have to respect his personal space and poke and prod at him until we get an opening to go in. Once we do get in Dedede beats him, either because we got an early kill from a smash or we got him off-stage where he does not want to be at all.