"there's still a good amount of learning the new kit to do before players are accessing Fiddle's full power." like what elo are champ testing Riot employees, if not even Challanger players has not figured out how you mean to play and wreck with him (as it is possible by Scruffy tweet)?
It is like Blizzard WoW test team all over again, having no players capable of clearing high end content and releasing unbeatable/undertuned stuff.
He's been out for 2 days. Every new champion goes through a period of learning where their average winrate increases over the course of ~ week. There are a few exceptions to this like Neeko, where it was harder to learn to play against her than play as her - her winrate on release remained pretty consistent and slightly declined over the week.