I still don't think there's any collusion. I think front offices in general are smarter so they're not wasting money. And the CBA rewards not spending, so there are more free agents available than there are openings for them at the prices they're asking. Teams know they can wait out the market and get a discount price in January or February because guys like McCutchen, Pollock, and Keuchel aren't going to sit out a season.
If teams KNOW they can wait until January or February AND that guys like McCutchen, Pollock and Keuchel are going to be around.... well, you would have just proven collusion.
The only way for teams to KNOW such players will not be around is if other teams, all of them, have agreed they are not going to sign them before then.
Otherwise it is impossible to KNOW they are not going to be around.... and even if all other GMs have said they are not going to sign them, it is hard to be sure some over anxious GM, wanting to get an edge on the competition, will not break ranks and sign them. That is the real reason collusion is unlikely to exist, the fact that other teams, each wanting to be a winner, will break ranks and sign someone ahead of the time others agreed to wait until, or for just marginally more than the others had agreed they would hold contracts beneath.
Competition is the strongest assurance against collusion.