They're seemingly already doing that for benefits. I've had benefits reduced at two separate places 'because our research shows we were a little over for similar companies.' If that's not collusion, I don't know what is.
No. Collusion requires agreement among the parties to not compete. Sure they copy but no one is forcing you to stay at the company or accept the new job offer. You walk to somewhere that does meet your ask or negotiate.
It's collision when companies agree to not compete.