G&W is like hugely about positioning. I mean you can argue that for a lot of characters, but I feel it's most obviously important on him. Spacing safely is all about maintaining that right distance where you can initiate without worrying about being in range of whatever oos options they might have. G&W's juggle traps can be perfectly devastating, but actually require a lot of skill to pull off right due to how specific the timing and positioning for his juggles have to be in order to be consistent. Landing raw Smashes with any safety or consistency also requires insanely good spacial reasoning to see where openings exist. And edgeguarding correctly is also about maintaining the right positioning where you have all their options covered with a particular move.
He doesn't have a truly instant mashable free damage button for many situations, given his moveset is built around sustained space control with slightly slower startup but low cooldown, so it's all about maintaining the right positioning with him to ensure you're at the advantage. This part about playing him takes a really high skillcap. Sure he can muscle his way through in some easy matchups here and there, although he can do more than simply just muscle his way through those matchups. Played right, he hits some matchups like a train wreck due to his capacity to really just perfectly capitalize on openings if he positions right.
So, how do fellow G&Ws perform at the Kirby matchup? I would certainly hope by now we proved it's at least 7/3 in his favor for example. That's just an example of a matchup that G&W really should never lose due to how well he really just gets in control, and never lets Kirby touch the ground again once he does. Aside from the many silly ways he can really easily set up free guaranteed kills on him.