Great breakdown.
Your description quoted above is the reason I labeled his style of play as "Hero Puck" as he lacks that team game chemistry. His athleticism and elite skating takes a front seat to team play. In the 2021 draft, there was a player similar to Fantilli such that their athleticism and gifted play didn't play well in a team game atmosphere because of "Hero Puck"; that player is Kent Johnson. IMO, Johnson has the highest talent ceiling in the 2021 draft, but has a difficult time playing a team game effort. Johnson is still developing that team game aspect.
What scares me is Fantilli's WCJ and playoff performances against higher level competition. At the WJC, he's darting everywhere like a whirling dervish and, like a whirling dervish, no one knows where exactly he's going. Fantilli's offense in the Big-10 and Frozen Four tourney against higher level competition got muted. Rugter McGroarty was the big producer in those games.
Hopefully, time will help improve Fantilli's team game, like you said. If he doesn't grasp the team game philosophy well, then he might be following Kent Johnson's path, which is to play on the wing. That elite speed, visual tenacity, and goal scoring brings lots of potential.