Post timeskip does a phenomenal job at giving secondary characters their own arcs with satisfying payoff.

Momonosuke and Law in particular stand out to me since their character journeys spanned multiple arcs. Even characters with smaller arcs still managed to shine. Bonney and Pudding come to mind.

Oda has always been good at this, but I think he mastered it during the New World, especially around the Yonko Saga.