I get a single digit gain. The facts are that with a pilot group the size of 6000 vs 1700, the whole thing doesn't move the system seniority that much for the SW pilots. That is not meant as a slight, or even a complaint, just the mathematics.
Whatever seniority hit you take is unfortunate, but it's the reality of a smaller carrier being bought buy one that's 3.5 times the size. That's a massive difference just in company size only.
These two companies are so different on so many metrics (size, contracts, bases, even the 717). The only good fit is the 737, and very little overlap on routes. And the slots that the SW corporation gets..
I would say the arbitor will most likely look at this ISL, maybe tweek it a little and toss it on the table. And for those that say they aren't supposed to know what's going on here, I would bet you they've already seen it. I know that they have already been very interested in what it looked like.
RF