Matthews is a Centre who drives his line and yes, scores a million goals(64 in his last 82 games played). And he plays a good two-way game.
Marchand is damn good, but relies on his linemates to drive the line, does not play the much harder Centre position, and doesn't come that close in the goals dept.
You can base it all on "points" but that's not what makes a player better than another player. Use your eyeballs.
Also........any ranking, anywhere on the planet, has Matthews ahead of Marchand. So THAT'S good too.