In 1998, when I was making $2200 a month instructing, ALL of the regionals paid less for FOs. I asked my fellow instructors basically the same question, "Why should we take a pay cut?" The answer? "The regionals are a quicker path to the majors." Well, maybe for those who chose the right company. I will say that going 135, who paid more than regionals, did not lead to a major for me. YMMV.
Oh, and the sitting reserve in XYZ issue: I would rather be at a second tier company with no commute than a first tier with a crappy commute. I would even look at a third tier if they have a stable (whatever that means) base in your back yard. But that is just me.