Yeah the writing was sort of on the wall when you saw the Dillon, Edmunson and Cole contracts. They needed the extra space to allocate to forward so were looking for defensemen in the $1.5-$2M range. Given that constraint, and the signing of DeBrusk, I think they did really well. Forbort was a value signing coming off injury, so they must think he's healthy, and with Desharnais the coaching staff obviously sees something (I think they're looking at him on the second pair, personally).
This premium on these guys sounds like it's connected to how they're coaching defense these days (based on Drance's article). It seems you put more responsibility on the forwards overloading support and taking the main responsibility for carrying/moving the puck up ice. The role of these big blue liners is to seal off the centre of the ice and get the puck to the boards for the forwards to win. I suspect this may be popular across the league based on the premium teams are putting on big defenders with wing-span who can seal off the centre and cross-ice stuff. The issue, as we saw in the playoffs, is you're a bit more susceptible off the rush with these guys, but if you can force dump and/or cycle you will bury teams with the size. Then you have speedy wingers on support that can win the battle and move the puck quickly up ice.