Leverage before a deal is done is based on perception of advantages, so Dak's interests are a big factor in that.
If he is completely okay with moving on from the Cowboys, that improves his leverage.
If the Cowboys are completely over with moving on from Dak, that improves their leverage.
As a fan, you are assuming the Cowboys want/need Dak more than Dak wants/needs the Cowboys, but that's an assumption or opinion rather than a fact.
The truth is it's quite possible Jerry is actually okay with moving on from Dak in 2025, and not as a coping reaction but a proactive action, so he is making a "take it or leave it" offer while not caring what Dak does.
It's also quite possible Dak wants to move on from the Cowboys so he is telling the Cowboys you either meet all of my demands or I walk and he is okay with either of those happening.
I think both sides have leverage, which I have stated from the start. I just think Jerry has more than people give him credit for. (Note: I did not say more than Dak because again, that's perception based on assumptions/opinions).