I agree with him needing to work on ways to be more effective with puck battles and clearing the front of the net. He will have to excel at finding the nest angles and positions to be able to use his stick to check as he just wont have the physicality to handle the bigger players in the NHL .
Im not sayimg he will never be able to so that , but he will have to be elite at other aspects of the defensive side of the game in order to be a full time defender.
Like how Spurgeon can be even though he is a smaller defender.
If Casey was 6’4“ and moved the exact same way as he does now …. He’d be a top prospect in the world , like top 10 IMO
But he isn't 6'4. He is 175cm player with, like you said, limitations in puck battles and in front of the net. He isn't very bulky too. So he is easy victim for 185-195cm top-6 players. Its just a question of lever. Luke Hughes should play with defensively reliable defenseman, so it push Casey out of top 4, or he needs to be so good to play with bigger defensive D and give stability to use Luke Hughes and Simon Nemec as a pair.
175cm good defensemen is a very rare thing in nhl, especially good two way defensemen, his puck skills could be very good, but we are talking about nhl realities, where defenseman should do specific work, there are a lot of situations where he will have no time and space to his stick as defensive tool. He needs to gain a lot of weight and learn how to use it, Or/and develop other defensive tools. Its a hard task to ask. He is very talented guy and I think he can develop, at least in some parts of his game, he is just isn't there now and physical aspect needs to change few steps more. He ist Will Butcher/Ty Smith level prospect, where even with points you can say that's an anchor, just pulling away this body from thr roster. But defense of contender should be strong. No one will have a tolerance to wait until Casey will figure it out how to not be outplayed two times per play off game. I think he is good nhl player potentially as qb, but its harder for him to earn top 4 job in NJ specifically, may be in most contenders. If he will be outplayed physically on regular basis, than he will have a lot of problems to be regular nhler.
So we are in situation with high risk high reward player. Its great to have him as a prospect, because I prefer players with bigger potential. They don't need to be small players as a whole group, but Casey is rare small player in our prospect pool, so it's okay. We just should admit not only his good sides of the game.