Great question. I know what he played like his rookie season that had me giddily expecting more and better to come.
If I look at what changed since then;
1.) I know he has been doing training each off season 2.) He has had several different coaches and presumably coaching styles. 3.) He may have continued to grow, mature andthat includes brain chemistry until I think I read 23 for males.
My snap summary; The coaching style changes and his continuing growth and maturation have messed with his head and how he was playing as a rookie. Second his current training regimen doesn't match how he has grown or the style of play we are currently doing.
He is failing with simple puck handling that was not a problem when he came into the league. So unless he has also had concussions that we have not heard about and any lingering effects he quite possibly is not the player he was as a rookie or he we thought he would be.