Except he's not your classic defensive dman, in fact, he's exactly built for the modern NHL. He's mobile and skates well, sees the ice and transitions with the puck either with a quick pass or by skating it out himself with speed. He's not going to be a point producer like the elite's in the game, but he has the potential to put up 25-30ish tertiary points like a Travis Hamonic.
Right now, he's hitting a rookie wall and not playing at the same high level as he was earlier in the year, but he's still very good; It's to be expected.
I think this is a good assessment of where we are right now.
Carol looked for the first bit of the season like a good young #3/4 defenceman who had a good first pass and played well in his own zone.
Over the last few games, he looks like more of a #4/5 (still good for his age) D man that has looked a bit out of sorts in the offensive end.
The question IMO is will we see him be the player who started the year or the one we see right now going forward. If he is the former, then he should be pretty untouchable. If he is the latter, it may make sense to move him for a upper echelon forward prospect/young guy while his value is still inflated.
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As a Leafs fan, I dont move Nylander (as some have suggested). He is too good and has proven himself at every level (SHL, AHL, NHL) to be pretty fantastic for his age.
Hard to compare a offensive minded young C/W vs a "modern" shut down D man, but I think Nylander has shown more potential over a longer period of time.