We don't have a true number 1?
That is correct.
Dez has way too many limitations which really limits the play-calling. He is not a good route running and the routes he runs are very predictable based on where he lines up. They do that to keep things ultra simple for him. He struggle to get separation on many types of routes which makes it hard on the QB, especially a QB with the low risk style of Dak.
They use TWilliams to run routes that should go to the #1 WR. Due to the limitations of Dez, they can't just use a burner as the #2 outside WR unless that player can also run all of the other routes precisely.
They are also limited due to Beasley's size and Witten's lack of speed. Both are great when used correctly, but it limits the Offensive Coordinator.
A true #1 WR would really open up things for the OC. Dez could then be a really good #2 WR for a couple of years until they move on from his contract.