One of the things posted/instatweeted is that his routing is very linear with a limited route tree, and another is what EJs brother's cousin's hair dresser's kinesiologist* mentioned about not seeing much at the top of his routes.
I've been wondering if the absence of a route tree is on Thornton because of inability/physical limitation or on coaching laziness because he was already open just going straight or on his QB who wasn't effective hitting him in straight lines and likely going to be able to find/hit him after a bunch of movement? Either way, get him a playbook, get him an invite to Jones' backyard playbook study sessions with his gf and see where he can progress to.
Even if all he does is go in straight lines effectively, he will still loosen the defensive box for the rest of the offense.
*Just in good fun
@Eddie Jurak - I'm envious at you having trusted professional voices in your immediate family. The voices from my immediate family seem to act in concert with the ones in my head, so there is that!