Tyson Barrie is only puck movement and little defense. Myers is a bit of both, and that's what they need more of. If that comes in the package of 'average or below sized' dmen, so be it. Players like DeMelo and Walker spring to mind as solutions.
It's interesting that people see the turtle/passive box strategy as being effective... It's what they had to resort to because they couldn't break the puck out of their zone. It looked effective while they were hemmed in because the bigger dmen could box forwards out. Getting puck movers is to avoid getting hemmed in in the first place.
The big D allowed the team to "protect the gut." Most of the season they did a good job reducing high danger scoring chances. So yeah, they traded defensive zone time for keeping shots to the perimeter, and it worked well.
What happens when a average or smaller d pairing doesn't get the puck out immediately? We even saw stretches where Quinn and Hronek would get stuck in their zone, and they'd get over powered around the net. Didn't happen often because of the quality of the players, but you're not finding comparable players (especially Hughes) on the free agent market.
But really, what you are asking for is a change to the defensive system. Tocchet wants players going to their defensive land marks, to protect cross ice passes, and keep the front of the net clear. You want a defensive system that recovers pucks and starts the transition before the other team gets set up. This team isn't built to play that way, and it's clearly not the style Allvin nor Tocchet want to run.
Think Allvin's comments about splitting Hughes and Hronek recognize the need to have more plus transition play on other pairings. But can't see the organization completely changing the philosophy that had so much success this season.