And that is what makes him underwhelming as a #1c. Prime Crosby scored 50 goals and 60 assists. Matthews scores 50 goals and 30 assists.
A center is supposed to make plays and support offense. Matthews plays like a winger offensively.
the interesting thing is, if you look at his production broken down by linemate, his two most frequent wingers were Marner and Nylander, but never together. Basically, he was centering one or the other. As Nylander has established himself as a solid goal scoring player, and Marner has established himself as one of the league's best playmaker's, it's interesting to look at the splits. When with Marner, at ES, he had 16 goals, 6 assists, 22 points. When with Nylander, he had 12 goals, 9 assists, 21 points, wiht nearly equal minutes. So, it isn't so much that he can't be a playmaker, he probably would have had closer to even splits with Nylander, as he would set up him more. But he clearly had a dynamic with Marner of Marner setting him up, and him burying it.
So, I don't think you can really say he can't be a dynamic playmaker, in fact, Nylander being put on his line seems to have been partly responsible for Nylander's goal scoring surge, but moreso, he can do both, and does do both, depending on the requirements of the situation. You'll likely see a 90 point player (likely more actually) next year, but the split on goals/assists, is probably more dependent on whether he spends more time with Marner or Nylander. You very well might see something more like 50/50 if he spends most of his time with Nylander.
You should probably also note that the 50/30 you reference was in a 70 game season, it would have been more like 55-60/35-40 this past season.