Sure you can. You just can't be stupid and pay for everything you "think" is talent. Everyone has the same cap at baseline, it's just a matter of who knows how not to waste it that determines the haves and have-nots.
An NFL without the salary cap (and as a consequence, a cash floor) in the era of TV deals being the highest single source of revenue doesn't work. Nobody is tuning in for a game that features a team with a $500M roster versus a $150M roster.
All teams have the same boundaries. You can't overspend, and you can't underspend. All teams face the same decisions regarding keep/losing talent. It's not like Dallas has been so blessed with drafting ability that they are inherently at a disadvantage when it comes to free agency based solely on an inability to keep everyone worth a new contract. You want no salary cap because you think that will give Dallas an advantage. Don't sugar-coat it. The salary cap is only detrimental to Dallas because Jerry and Steven absolutely suck at managing it. They haven't picked up a big, outside free agent, contract in nearly a decade and still have the salary cap problems they had in 2012. Always over, and now going back to restructuring for the sake of being compliant.