Well here's the issue, 6 year contract, average $26.66 mil a year. Right now someone like Stafford, who's hardly sniffed the playoffs, averages $27 mil. Cousins? $28 mil. Just what will a top quarterback cost in, say, 2024? I suspect upwards of $35 mil a year, or more. So locking Dak in for $26.66 mil means (assuming he develops into a top qb, or the team does and he's the starter) he'll be a bargain in 2024. And with the cap going up it's average for the last 5 years, about $8 mil, that means by 2024 the cap will be at $217 mil, so Dak costs the Cowboys only about 11% of the cap.
That's the rosy scenario.
On the other hand, if he gets better and you don't sign him, his value will be more like $30 mil, since the top qb salaries go up just about every year, and who knows what the team will need in another year? Zeke gets a chronic injury, Freddy's GBS flares up and he has to retire, Martin's shoulder goes out, etc. and now you need help big time, right NOW.
Of course you can sign him, and if he never gets better, or gets worse, you've got another Romo on your hands, dead cap eats you alive.
That's the doom and gloom scenario.
Really a shot in the dark, actually Dak not improving is at least a bit more likely, he's had 3 years in the league and still has some of his same issues, though Moore maybe can help him there. Just another unknown.
But one things for sure, whatever the Cowboys do, a lot of folks here won't like it!