How many times did Kelly publicly push DD this preseason? He's solid but has not shown his NFL caliber skills-he's not a lock. If he improves, sure he could make it happen but he is a blossoming project (get healthy DD!). TJ is a starter and yes he can catch the ball-but realistically, he's a safe bet for Kelly. he's proven that he can play mistake free ball. However, TJ seems to lack explosiveness.
Here is my take on DD, which I expect some people might scoff at it: I think DD was a little scared of D1 competition, the spotlight, the physicality, etc. Watch his interviews from last spring until now. I always thought he looked like a dear in headlights, and he is only now starting to lose that look. Now he just looks chill.
He has Tier 1 talent, but he went to a high school where he was a ton better than everyone else. He also has an NFL father, so I think people expected him to be tougher than he really was. This is not to say that he did not have self-confidence in his potential. He apparently always knew the tlaent was there. But I don't think he embraced the game the way other players did. Cierre Wood had a similar process. D1 was a wake-up for him, and he did not look like he liked the physicality until the end of his first year playing.
Long story short, I think it is all about swagger with DD. Like Ishaq Williams, when DD stops thinking so much and just starts playing all out with confidence, WATCH OUT!
On LT. If he were to come, I could envison TJ or DD sliding into one of the other spots to let him play boundary, especially in spread sets.