A greenfields agreement is assessed by Fair Work against the Air Pilots Award 2010 which definitely my and presumably your union has participated in and accepted. I'm no expert but E190 terms and pay must be par or above otherwise it would not have been accepted by Fair Work. Feel free to bag the union for their role in the Award and go as hard as you like on Alliance but hold off sledging individuals for making decisions they are entitled to make. Pretty simple if others don't agree with the terms Alliance have on offer they don't have to sign.
But do they have the right to agree an behalf of all pilots? If someone wants to take a cheap deal for themselves because they have a inheritance, bitcoin, money stashed in a Swiss Bank, the company gives them special share options etc etc that's their business. However the majority of pilots need to make money out of flying and a downward trend is really starting to appear in the industry. Also worth noting that no business actually agrees to the full award as it is way to restrictive. They just cherry pick the nice cheap bits they like then conveniently ignore the expensive/difficult to implement parts. Just like all the GA operators who used to claim they paid the award. They might have paid the salary but never any of the allowances!