NFL doesn't have a system for parity. Not intentionally, anyway.
NFL parity began when Offensive Lines stopped playing together for several seasons. When a team can get an Offensive Line to develop continuity through time together, and it takes several years together, then a team can establish consistency with their Offense and dominate opposing teams from year to year. That all gets thrown out the window because of the current free agency system, where a team can't afford to keep an O-Line that's good together for more than two seasons. No team can hold it together for three seasons because of Free Agency costs for quality O-Linemen. You can keep two, maybe three (at the cost of going cheap at some other position that weakens the team), but two or three O-Linemen will constantly be changing and that's going to make it so that there are never any elite teams again. One team will get hot for a season because they went all-in, or they managed to survive the long season injury-free (another reason for parity is that there are always missing key players every week for every team), but they'll soon fade like the Rams did this season.
This is why I love the two FA signings of Cappa and Karras. We bought quality with upside of Linemen who fit our schemes at mid-level prices for the positions. Even the RT acquisition had a lot of upside (and it showed in the run-blocking) while the cost stayed at a mid-level price. We are still in position for our Offensive Line to pay for a quality LT. Williams may be best used at RT, but his play is pricing him off of the team as he'll want more than he's worth, and he's not worth more than he is. He doesn't seem to have that kind of upside anymore.