Skywalk, armament haki, observation haki, easier time using Diable Jambe and now on both legs no spinning and Hell's Memories. Timeskip laid the foundation for further growth and for his new powerups. Plus, they put him at a level where he can keep up with formidable dudes in the New World and protect those he cares for even if he doesn't defeat his enemy (Vergo, Doffy, Daifuku, Oven). It wasn't a waste, dude literally one-shotted a Pacifista and fried Wadatsumi in one hit then kept that move in his arsenal to be used again when appropriate, Wano. He clearly improved, it wasn't a waste.
He wasn't strong enough to beat Commanders straight out of the timeskip but he didn't have to, he just needed to be able to handle threats that came his way and protect his friends which he did a goof chunk of the time. The recipes were used at Punk Hazard and sadly, there hasn't been much focus on them but his cooking skills are pretty much superior to anyone from Big Mom's crew so he definitely improved.