The limits are in place to:
A. Save smaller markets.
B. Maximize the earning power of the majority of NBA players who would vote for changes in the CBA. If the BRI split is such that it limits the total money going to the players, with no limit on max salaries teams would be playing the stars so much more that there would be so much less available to most of the players.
C. Save the owners from themselves because they have been shown to make really stupid contract signings over many, many years.
That is what the actual team salary cap is for. If you still have the team salary cap, then it really won't affect the smaller markets as much. So a team still either has to have the player on its team or have the cap space to sign them. Now I do get the idea that if you pay Giannis what he is worth that is less money for the George Hill's of the world, but so what. Giannis is worth far more than he can be paid, while Hill is paid far more than he is worth because of the way the current system works. Balance that out, and I think you see a lot less top end player movement.
So you want the NBAPA to vote to give the massive minority of players almost unlimited earnings, so that the overall massive majority of players can take a massive pay cut so that player movement of the massive minority of players don't move around as much?
I don't think it would be as dramatic as you make it out to be. The vast majority of the leagues salaries wouldn't change because they are on rookie contracts, veteran minimums, or MLE type deals. It would affect some of the players that aren't MLE type players but not max level players, but I don't think there are all that many of those (at least not dramatically more than the max level players). Frankly, I don't think a single Celtic would have had their contract affected by this change, other than Irving going up and perhaps Hayward or Horford actually going down (when there is no max then teams also aren't hamstrung by paying max to players that don't really deserve it).
Of course, players on current contracts would not be affected. A new CBA, as you discussed, would be affecting all new contracts of veteran players, with superstars making the vast majority of the money and the rank and file suddenly being low balled. What you are discussing will affect those players paychecks....eventually, not right away.
It really is very simple logical math. If the players only get a certain percentage of the pie, if with new contracts the superstars are getting a larger piece there is a lot less available to give to all those other players.
There is now way LeBron and Chris Paul, players making ridiculous money, are going to convince the players it is in their best interest to allow superstars to make way more ridiculous money, when they would have to be giving up money to do so.