I really like the way you think and have so eloquently stated in this OP. I think it has merit. I want to buy into it. I truly do.
But in ALL SERIOUSNESS, you already have to assume two things:
1. Slow as molasses Witten is going to be short of the sticks ( but he will catch the ball).
And
2. Dez is probably going to run the same two routes and drop the ball about 1/3 of his catchable passes.
So that leaves the other receivers to do something different. I think they can --and will.
But wouldn't it make more sense (since it appears we are keeping Witten) and go with the same old, same old there----- to cut Dez and get another receiver who will run a route?