The Group III pay issue, on the surface, seems to be a very bad deal. And in some ways it is. But let's take a step back and look at the whole picture.
Currently, international flying is done by the B777, A330, B767 and B757. Most of the long-range stuff is Group IV only, with a few 767 routes thrown in there. That international fleet is about to get up-ended as the B767 and many of the B757s retire. Some of the 757 fleet will remain in service for a while longer.
The company has B787 and A350 aircraft on order (and a handful of B777s on order). While a few of these will replace some of the older B777s, others will be replacing the 767 fleet. As the 757 fleet begins to pare down, the A321neoLR will likely replace it on the routes.
So that leaves us with the 767 and 757 positions moving to Group IV and Group II. There's a strong argument that the A321 should be a Group III aircraft, and I think pretty much everyone agrees with this. The problem is, the company has no interest in changing it, and there's really no mechanism in place right now to change it.
So where does that leave us? Voting yes or no will NOT alter the course of the fleet evolution. We WILL wind up with mostly Group IV and Group II aircraft and only a handful of Group III aircraft. If you vote no, you'll wind up with the MTA rates and Group III jobs will still gradually migrate to Groups IV and II. Looking at the TA pay, a Group II FO will make about the same as what a Group III FO would make under the MTA. And even if Delta gets better than what most are expecting (around 5-10% raise), Group III FO rates would only be marginally better than Group II FO rates (by a couple bucks per hour). Plus, some of those Group III positions will wind up being Group IV when it's all said and done. So while it's not ideal and not what it should be, it's not the end of the world either.
Voting no will not stop the A321 from taking over some of the 757 routes. Voting no will not make the economic situation better. Voting no will not somehow magically force the company make the A321 a Group III airplane.
I don't know when APA sorted out which aircraft would be in what group, but I think it was a huge mistake to arbitrarily throw the A321 into Group II just because it belonged to the A320 family. But that's all water under the bridge, and honestly at this point we're not going to see that change anytime before 2019/2020.