They had to as it was required by arbitrators award. No new-hires and most current F/O's aren't part of this and must rely on a contractual agreement that is far less certain.

If things don't pan out at Envoy with the flow (which logjams upgrades all over again), is it better to just be the latest sap stuck in the right seat at Envoy waiting for another promise to materialize or somewhere building 121 PIC and captains bucks ?

I say the latter is the better bet until AAG makes a rock solid commitment and not Envoy management and your promises.