I get your point. However, CeeDee is by every list I've seen no lower than the 3rd highest rated WR. He can ask for top dollar because he's at or very near the top at his position.
Dak, on the other hand, is by most lists I've seen somewhere around the 8th or so ranked qb. Plus, as the qb he has much more input into winning the games than CeeDee does, and he hasn't performed well in the playoffs.
So Dak imho can't ask for top dollar, CeeDee can. Also, if no CeeDee how can the Cowboys get another top 3 WR? They can't, drafting one is risky and doesn't usually produce a top wr for at least a couple of years, and any free agent WR as good as CeeDee will cost just as much as CeeDee is worth.
And thought he might not be Dak, Rush has performed at least serviceably when he's played, going from Dak to Rush would not be nearly as big a drop as from CeeDee to say, Tolbert?