By all accounts Mason is excellent mentally, forget the level for a second, sometimes it's just too obvious like it was with Bale and KDB when they started out. Mount's speed of thought and impact on games is galaxy's ahead of Musonda, McEachran etc, it's worth noting that Charly went on loan to a weaker league and epically flopped.
The maturity and intelligence in Mason's game is down to him, not the Eredivisie.