Recipes, Luffy and Crew wouldn't be as strong as they are up to Wano without eating Sanji's food when he was around. Even if we don't see it, as that was Sanji's whole thought process (and making the girls more 'sexy,') we assume he started using it consistently.
Leg strength from fighting martial artists and indirectly running constantly.
Sky walk and hell enough to create Hell's Memories.
But the biggest one I think is lack of distraction. Sent somewhere with no women, crew, or anyone normal in his eyes makes him work harder because there's nothing to get distracted on. No islands to save, no women to lust after, no people to feed, no other events to get caught up in. Just focused solely on training and self reflection (he had no one on his side as true allies or friends, a situation he hadn't been in since before meeting Zeff, so that was probably a mental stress to learn to deal with.)
Which is another reason I absolutely hate the anime filler. If we take the filler as canon, had the newspaper not came to snap him out of it, Sanji would have stayed hypnotized into having lost himself, no training and no improvement.
The cover story just showed him forced and pretending, still internally himself (veins of anger) so that wouldn't have been an issue.
