PG,
Using your sandbox example, even the most ardent ALPA supporter will struggle when explaining how it's a good thing that Pinnacle reached a deal that places a "reserved for us" sign in that part of the sandbox. That makes that part of the sandbox permanent.
Your point is well taken that the sandbox is shrinking, of course.
The DPA would have you believe that national is somehow coercing mainline MEC's to give up flying, and enlarge the sandbox. To support this idea, Carl (as an example) recently said this:
DALPA doesn't control much of anything. The money taken from our paychecks as union dues goes straight to ALPA, and DALPA gets a portion back administered by ALPA. If we decide to fight against something (like outsourcing), we'll first have to fight our own national union who has clearly decided that the wealth of flying jobs MUST be spread out. They can simply not fund any actions we might want to take against that, not give us legal help to do that, not give us contract language help to do that, and many obstacles they can throw in front of us.
I don't think this description is plausible.
On the other hand, you do have a case here where another group did carve out a piece of the sandbox. Bar has hinted that there might be a reason for this, but I don't know what that is. It doesn't seem like the information is going to forthcoming, maybe for the right reasons.
In that case, I think you've got to accept the legitimate skepticism of the Delta pilots, and fess up that a deal was made, within the sandbox, that we don't like. It shouldn't happen again. OR you explain why the deal was acceptable in other ways. OR you can provide another credible explanation. At a minimum, you have to acknowledge the concerns many of us, ALPA supporters or not, have.