I’m as giddy about Dahlin as anyone but he is not the best dman on this team at the moment. He is 18 and gets a pass for a lot of stuff that the other dman get hammered for. As he cleans those things up and plays tougher minutes he will grab the title of our best dman. But he isn’t there yet.
I think it's fair to project his performance with Nelson out a little bit. While they're currently a sheltered third pairing, they're driving the type of overwhelming results that can scale to more difficult situations, think Nate Schmidt's transition from Washington to Vegas.
And given his competition has been Bogosian and McCabe, they have the same sample size of games as good NHL defensemen. Tiers for the season probably look like:
Dahlin/Bogosian/McCabe
Nelson
Scandella/Risto/Beaulieu
It's hard to rely on 75% of the current top 4 by performance to sustain things rest-of-season. Pilut/Guhle definitely help guard against some of the expected regression, but they're most likely to replace Bogo/McCabe, which means high leverage minutes with one of the team's bottom-rung defensemen. Even if they're swapped in for Risto/Scandella, it's not like McCabe and Bogo are historically easy to play with either. Pilut for Scandella/Nelson is probably the one move that makes the blueline definitely better.
Long-term, there are two smart plans and one dumb one. The first good idea would be to swap Scandella for a player who can take on tough minutes on the right side. Scandella's expiring contract might be more valuable to a bad team that wants cap space, plus he could be a better deadline asset than a multi-year deal. That would get Risto away from shutdown minutes and into an offensive role with one of Dahlin, Pilut, or Bogosian. The other two (plus possibly Nelson) would play clean up.
The second, is getting a high end partner for Dahlin and cutting him loose in top pairing-ish minutes (we should probably keep things more offensively skewed than your traditional "top pairing" for now) with the proper support. That at least keeps 55's minutes down if he's going to stay in a shutdown role, or slots him in as a #5 who can play up the lineup on his good nights.
The dumb idea is pumping assets into the Ristolainen pairing, either by trying to get him a shutdown partner, or a puck mover to drag him along in transition. The team is dangerously close to living the dream of not playing Risto out in every situation, and it would be disappointing to find out they still view him as the Pronger to Dahlin's Niedermayer (or whatever).