I could be wrong, and probably am, but wasn't it common practice to give these long contracts with an understanding that the player would either not even see the last couple years, or it would be renegotiated sometime in the last couple years?
The long contracts provide maximum cap manipulation opportunities.
Yup, except I would say it was heavily in favor of the team/control. Most players decline within their 2nd contract. So, it would make sense for teams to move on in year 3 or 4 of a 5-6 year deal as the dead cap would(should) be under that years cap hit. And while dead cap would stick over 1-2 years, depending on cut designation, the team didn't usually pay out anything.
Teams use the length of the deal to restructure and spread out the cap hit from the new prorated bonus as far out as can be. Recently, teams have been adding void years to be able to stretch out the cap hits while not actually extending the player longer. It really took off after C-19 and the reduced cap/flat cap.
Dallas did it at some point with Martin. Doesn't negatively impact the player in any way, as the contract voids as soon as the "original" extension ends.
Restructuring 11 mil over 4 years(including current year) is a lot nicer than 2 years when the cap hit from the proration knocks out a lot of the "savings".
But yes, some deals are artificially long to inflate the AAV.
Previous example is the Tyreek Hill deal. He will never see that last year. 40+mil base salary with no guarantees = cut prior to week 1 or extension.