Earlier quoted context omitted.
Another large part is the draft. Worst team gets first pick goes a long way to levelling the playing field.
As a lapsed NY Jets fan, I disagree -- competent ownership and management is required more than good draft picks. To wit: Tom Brady was drafted at 199 overall, but the Jets' last two QB picks (Zach Williams and Sam Darnold) are both journeyman-level players. I'm more of a hockey guy, which has a much stricter salary cap than the NFL, and the Edmonton Oilers are instructive here: they had a bunch of first overall pick…
In the NFL, winning is more about quality management and coaching (and some luck) than anything else. Which is a good thing. Leagues where winners are decided mostly on who is able to spend the most on players are lopsided and kind of lame.