The difference between the Pens duo and the Leafs duo -- and even the Oilers duo -- is that they had a killer instinct and mental toughness to persevere. The same with the Blackhawks duo (Kane and Toews) -- they just had the "it factor" and a superior ability to rise to the occasion.
Evaluating Matthews and Marner -- at this point they still have major flaws that show up in meaningful games. Matthews is an elite shooter but when the opponent attacks his space, he vanishes. He doesn't have the acceleration, jump, intensity and fight in him, to just grab the puck and dominate the way a Crosby, Malkin, MacKinnon, etc. do. In the playoffs, Matthews turns in Patrik Laine -- floats and looks for chances to use his shot. Sorry, that doesn't cut it in a Game 7 for all the marbles.
Marner continues to dance and dangle but has nothing to show for it, because the lanes clog up in the playoffs and the other team's D is all over you. The only way you defeat that is to up your intensity and focus, the way young Crosby and young Patrick Kane did. I know it sounds cliché, but these kids need to "want it more."