Scheifele is a franchise 1C. He is substantially more valuable then Monahan.
I don't know if he is quite on that level, but he certainly is a legitimate 1C, though he is miles ahead of Monahan.
I would consider guys like McDavid, Crosby, Malkin, Eichel, Mackinnon, Barkov, and Matthews as franchise centers.
I think in order to be a franchise C, you have to have be a multi-dimensional threat. I don't think Scheifele has enough dimensions to his game to be a "franchise" center. I think the particular dimension he is missing is his ability to carry the puck and dictate the pace, but he also isn't the strongest defensive center (in part because he lacks a bit of agility and foot speed).
He is a solid 1C though, and one of the best PP triggermen in the league.