We lack a big physical guy long term, Zub is physical but not big, Sanderson might become more physical but again, not big.
I think you could build a D around Chabot, Sanderson and Karlsson, but you'd need to have some size and physicality to round out the group.
Could you add Karlsson and seone like Carlo or Mayfield? Or both if we can't get Zub extended?
Chabot-Karlsson
Sanderson-Mayfield/Zub
Brannstrom-Carlo
A D group like that likely costs us the flexibility required to re-sign DeBrincat, but it seems like a pretty strong group.
I don't think Karlsson is the answer, imo we'd get diminishing returns out of both Chabot and Sanderson by adding a player like Karlsson. I think we'd get better bang for our buck just adding those physical Dmen I mentioned