This change looks like it's targeting players/bots that just run down their ECR in search of rating. Does look like a nerf disguised as a QoL upgrade.....
Rewards wise, I think only time will tell because the SPS rewards are from a pool, so if everyone is getting 100% all the time, the pool should deplete faster as well. Whether that is offset by the reduction in games played, that will take a few seasons to pan out. Also, less games played is not a good thing if that means taking longer to match-make.
Everything SPL does has a butterfly effect.....good or bad, we will never know till the next change.