For me, the problem with Sandin is 50% the player type, the player himself and 50% the blueline construction and why it would never work here.
Let's say the highest ceiling on a small, slow, not strong and high IQ defenseman is Adam Fox, a Norris Trophy winner who puts up star forward numbers.
Look at the Rangers blueline. They've insulated him with big body, length defending, two way, physical defensemen Trouba, Miller, Schneider, Harpur and another really tough defenseman in Ryan Lindgren. There is so much protection and backup so Fox can do what he does well without being burdened to do the physical work on the defensive end.
Going back to Sandin, he isn't Fox, he wasn't patient to develop in a supporting role. He wasn't capable of supporting the blueline mix, and the blueline mix wasn't built to protect him. It was a bad fit, he didn't want to fit, so move on.