I mean that's fine, but Owners aren't going to absorb risks that they don't have to. If they went with fully gtd contracts, the contract lengths would be much shorter (i.e. most players would never see beyond a 2-3 year deal) and there's a zero % chance the Owners would do it without mitigating that risk, i.e. giving the players a small piece of the Revenue pie.
Other sports are OK comparisons, but those sports also generally have longer average careers and less injury risk than the NFL. Not to mention that, in those sports, especially true of the NBA, the high-end players dominate the earnings pool proportionately more than the bottom-end earners do, and so the majority of NFL players would end up making less $ overall.