B767300ER,
Lets imagine American Airlines is bankrupt and pays less than 1/2 that SouthWest Airlines for years, but is still hiring primarily due to age 60 retirements. Now imagine a pilot getting hired at AA then a few years later they are bought, (not merged), by Southwest.
If I was that pilot I would hope that my "reality goggles" wouldn't be fogged up enough to realize I shouldn't expect a relative percentage merge of the seniority list. This would be especially true if only a few International routes are retained while the rest are discontinued, along with another commuter carrier other than SWA's pilots operate much of the short haul domestic.