People have to quit getting bogged down with the fact that Dak will be among the higher paid QBs because it's not a function of value relative to other QB's who are under a current contract, it's a function of the market at the time the contract is being negotiated.
If Rodgers, Roethlesberger, Brees and others were negotiating contracts today, they would get significantly more money than they are making now, and significantly more than Dak would get. But that's not the timing. It just happens that it is Dak's contract, and not theirs, that is coming up. In a year or two less productive QB's than Dak will likely end up with bigger contracts than Dak's because they will have to be paid relative to the market as it is at that time.