Dez is the type of player you have to keep engaged or he will lose interest.
HOWEVER, I will say this. Dez route running is garbage. He rely's way too much on raw physical ability.
Most of his catches are low percentage scenarios where the probability of a completion is less than 50%.
With that being said, his presence ALONE opens up the field for everyone else because defense will still draw the coverage to his way. As long as the QB doesn't try to force him the ball, the offense will stay in rhythm.