Deep threats like Smith don't come around often, so to expect him to be Devin Smith would be hopeful IMO. I would find a middle ground between Possession WR and Deep Threat and call him that because I think he runs very good routes and has the speed to match. In the MSU game, he beat the corner inside on the slant and then he outran Kurtis Drummond, who is an NFL player and didn't really take that poor of an angle. In the Oregon and Wisconsin games, he made short catches and turned them into 20+ yd gains. Moreover, Thomas beat Maryland's top corner deep and had Oregon beat deep, but couldn't stay in bounds.
When I think possession receiver, I think of Wes Welker, Julian Edelman, Jason Avant or Anquan Boldin who run quick, short routes, exclusively, because they don't have the speed to beat a defender deep and often get limited YAC due to their lack of speed. Thomas can absolutely be a deep threat, with his height, physicality, speed and strong hands. Anyway you characterize him, he is dangerous and one of the most talented WR we have had here in the last 10 years.
Plaxico Burress was a heck of a deep threat, just ask Antoine Winfield, and did not have elite speed.