You know, you could have made the same argument for Bedard in 21-22 - that he was trending downwards, especially with his weaker performance at the u-18s. But know what? One season isn't all-defining and doesn't mean that the player suddenly stopped improving for good.
Actually, if I compare Kiviharju's season to Bedard's, I'd say that Bedard had more of a downwards trend. Kiviharju had a stronger u-18 tournament, while Bedard's was weaker, for example.
All that is to say, maybe 1 season isn't enough for drawing conclusions regarding trends.