It probably wont be, but the Cowboys have 3 options.
1) Eat the bulk of his cap hit now and create more flexibility next year or even more leverage in contract negotiations.
2) Restructure the deal push money into years he isn't even on the roster.
3) Extend Dak at an even higher AAV....the biggest piece here that worries me is that you are negotiating with Dak at a time when he has total control. The Cowboys need to get his cap number down and the first two options are not that great.
I think you're right that Dak's cap hit wont be that high, but I'm not sure the options to lower that hit are that great.