Marner has been a better possession player than Nylander for a good while now. No reason why he can't do the same with Matthews.
Babcock is trying to turn the team into a more dump and chase team and so the Matthews line is much better at winning puck battles and getting the puck back after giving up possession and a lot of that is due in part to Hyman and his dog on a bone attitude.
The Bozak line doesn't compete hard enough to dump pucks in and then go get it again , and I can't see Babcock asking Marner to ever be the first man into the corners or battling in Dmen behind the icing line to regain the puck... Marner drives a line offensively but likes to carry the puck and dangles with it, where that leads to better possession #'s, but when the opposition clogs up the ice and disrupts the attack it can also make a rush line less effective. Babcock doesn't want the Matthews line to be a rush line.
It will be interesting to see what happens with Marner if Leafs walk away from JVR and Bozak this summer and who his new linemates will become. I think Babcock like will keep the Matthews line intact as is, and Connor Brown might replace Komarov on the Kadri -- Marleau is uncle Leo moves on.