Tannehill, from my limited experience, looks different from game 1 to game 12. That's a positive. I was seeing more zip on his passes towards the end, and much tighter throwing lanes. I attribute all of this to his footwork, but I'm looking on freakin Youtube so it's pretty hard to tell.
Watch a guy like Drew Brees. He is consistent with both his placement and velocity... Tom Brady is as well (actually, Brady is the literal poster child for mechanics) but you'll see that it's simply due to their footwork and mechanics, as well as hip movement. Tannehill has a lot of erratic throws his junior year, and I see a lot more consistency in his later years. I also see a lot better timing, especially with that little WR they have, Swope.
He seems too eager to run out of the pocket, IMO, which is troubling for me. That will get him killed in the NFL. He needs to find a lane, stick to it, and just let er rip. I hope he has the natural instincts which seem to be absolutely key to becoming elite.