Look at how much he's producing. That's not really a stretch. That doesn't make him the 2nd best player in the league, it means this season he's playing like it.
But his play is not that of the second best player in the league. There's several criteria where he's behind the likes of Burns, McDavid, Kane, Panarin, Hedman, Malkin, etc. To some, he's not even the best rookie in the NHL. I find that kind of evaluation amusing, but it depends on how much weight you give certain aspects of the game.
I'm in the "it's only been half a season" boat. The Matthews we see today could be that much better as he gets older and the surrounding players get better.