Players play with whomever the coach tells them to play with so it's a moot point as such. Each reliies on the other as long as they are on the same line.
As it were, they were both highly touted. 1st and 4th picks overall in their respective drafts. Marner was second in the OHL in points, Matthews had a unique career on the way up, his work on the International stage and playing in the Swiss league (how lucky are the Leafs that he didn't go in the 2015 draft? They couldn't pick both players).
I do believe that if they stay together their entire careers that the Leafs record book will have both of their names up top, along with a couple of Cups almost certainly. The Oates/Hull of our time, though hopefully for much longer (imagine Oates career totals if he would have been working with Hull for the years he helped Neely?).
Hell, we might be comparing them more to Gretzky/Kurri at some point. Win some Cups and these guys will live for eternity in Toronto and the comparisons won't seem so outlandish.