Although I think Dak is a very good QB with potential to become great, it is no means certain. Brady & Mahomes situations are nothing like Dak's. The 2 QBs situations that are VERY much like Dak's are Goff and Wentz, and we see now how both their franchises have regretted paying them "Market Price" at the time.
The odds are good we will be much more likely to regret the market value contract like the Eagles and Rams did because UNLIKE the Bucs and Chiefs with Brady & Mahomes, the rest of our team isn't a QB away from being Superbowl contenders. We need too much help with our defense. Neither Brady nor Mahomes could win a SB with our defense as it currently stands. We need to build it up. Very hard to do with paying a massive contract to your QB.
Paying Dak means we have to be much much better drafting defense than we have been so far. It is not impossible to accomplish with a highly paid QB sucking up so much of your capital, but you have to be extremely lucky and hit on some real later round gems in the draft.
Or, you could structure other contracts to open up a year or two window to spend on free agents to go for broke at that time, messing up your future cap and making it virtually impossible to win even if Dak becomes the best QB in the league after that.
Cowboys are at a very unenviable crossroads. Pay Dak and hope to be extremely lucky in the draft to build a contender or let him walk and have an easier time to build up the roster but likely have an inferior QB/Leader to helm it.
Either way, I will support the decision as neither option is great and either option could turn out well in the end. We will see.