Problem 1: Purchase of larger aircraft.
Once you get past the first few dozen pilots at VX, the average age of a new hire started to be lower than AS. Let’s just assume to prevent an argument that the average age of a new hire was the same at both companies throughout. All of the AS pilots on average are paired with pilots of about their same relative age, however because VX pilots get put in with pilots that were hired 15-20+ years before them it is as though they were hired by Alaska when they were 15-20 years old (15-20 before age 35 years of age which is my guess of a historic mean of new hires at AS). Over time, the top of the combined seniority list will start to stack with VX pilots. I’ll just take myself as an example, I was to retire AS at about number 30, now it’s looking at about 160ish depending on who wins the arbitration. The majority of those pilots being mostly VX guys and all of them hired at VX after I was hired at Alaska. Now if AS finally orders say 20 787’s, I would have been a shoe-in to get a slot without the merger, since the merger, I probably would not get a 787 slot.

Problem 2: The California plan doesn’t work out.

Let’s use the example of a mid-seniority Captain. Say 25% at Alaska that puts his seniority number pre-merger at 500/2000 (let’s pretend for math sake) if he maintains relative position then he is post-SLI at 700/2800 (25% again, let’s pretend for maths sake) . Now this California plan doesn’t work out in the next few years and we end up right back where we started as far as total number of pilots. Well now, the Alaska Captain is now 700/2000 which is back down to 35% which takes him from a middle seniority line holder pre integration to barely hanging on to a line. All 200 slots above him would be lost to pilots that were hired at VX 5+ years after he got hired at Alaska.