Well, first of all, I see Byram playing on the RD all the time, and not Dahlin, take a closer look at the games, Byram is on the RD much more often than on the LD. Secondly, they are also not ideal in a pair, I see a lot of these small mistakes when they get confused about who should be on the RD, and sometimes both are on the LD, and the opponent's forward easily finds free space because of this.
I don't see the point in three PMDs, this is excessive, we need more defensive right-handed defenders and a top 6 C and other positions . So trading one of Byram/Power makes a lot of sense for me.
But even if Dahlin is more comfortable playing on RD and he wants it. Find him a more defensive partner, as you said, a vet maybe. Gavrikov, M. Pettersson and etc. Although Ruff literally said at the beginning of the season that he needs two RDs in the top 4. And in general, if you look at other teams, most of them have a balanced defense of PMDs and defensive guys and three right-handers and three left-handers.