The point you're missing is that he is certainly one of the first names down on the team sheet, whether they know what position he'll be playing or not.
If Hook is fit he starts for Wales. Fact.
Utility players start on the bench.
I will accept the vague half point that you're making ie: that he is a victim of his own versatility, and his development might be simpler if he played one position all the time.
But your suggestion that he is undervalued by the coaches and that they wouldn't be bothered if he wasn't available is ridiculous and is going to get treated as such.