I think the question is more who was pushing for this. I think the answer is that the NBA owners needed to reign in escalating spending by teams. There were issues with regional television networks and other issues that were evidence of stress cracks in the system. The NBAPA didn't want a hard cap. So they created this as a way of creating a cap without having to call it a cap. It seemed to satisfy all parties.
I think in the end, the players are not going to like this and the owners are not going to like it. The fans don't like it either. To me, the main problem is that the max and super max contracts are too high. Once you sign 2 or more of these contracts, a team does not have enough money left to get a good roster around these players. Way too many players are getting stuck with MLE contracts or less.
BOS was a team built around 2 max contracts and some well paid veterans. That team had to be broken up. Then you get teams like OKC who have their best players on rookie or first non-rookie contracts, much more cost controlled. They got lucky with SGA but they will have to pay him, and everyone else. Veteran teams are going to have a hard time being competitive. There is no way to afford a veteran team anymore.