IMO, that's precisely the problem with their core. They NEED to play with one another because they're not the type of players who can play with two scrubs and produce.
That's what made Sid and Geno so special. We could spread the talent around because those two could play with the likes of old man Guerin, Fedotenko, Talbot, Sheary, etc. and still go deep in the playoffs. Matthews NEEDS either Marner or Nylander on his line to generate those chances because he's not the type of player who will be point per game if he's flanked by Laughton and Jarnkrok (for comparables to the guys Sid and Geno played with during Cup runs).
And IMO, Tavares has always been overrated. He was made out to be this elite, almost generational player when he was much closer to a point per game, "good" player. And he's even worse now that he's old and skates like Joe Thornton. He'd be lost without Nylander carrying the puck for that line.