How many can the 73-9ER seat? Not company chosen config, but max certifiable, which I think is the yardstick for the seating metric in the speed/efficiency/payload/whatever formula. I think the 73-9ER seats less than the 757, which means we will need more 73's to move the same number of people.
Of course we could (probably will) continue to shrink so we can keep funding the order books of the ULCC's and our west coast 737 ACMI regional feeder
but even in that case we were going to shrink anyway so if the 757's never went away as a fleet we'd still be parking some of them to dicipline the capacity or leverage the synergy or whatever term the latest $300 regurgitation textbook calls "shrinking our way to profitability" in B school this semester.
So while we will be replacing 757's with lower paying 737's, our 737 pay is still a lot higher than pretty much anyone we have a remote chance of merging with. That is still one factor that will remain and be a part of the "career expectation" model. If we buy Kalitta there is no way in he11 a 2 year "74 Captain" making our 3rd year narrowbody FO pay and less benefits is going to slide on over in a full relative with where it takes to hold that seat here. No way, ever, no matter what. Pay will be used regardless to some extent as will many other factors.
Likewise, some of the 737-900ER's will be replacing older A320's (40 I think?) which will be a pay increase for that lift. The real wild card will be the ramaining 320's but especially the MD88's. C Series? 73MAX? Bigger "RJ's"? Mo' Shrinkage?
I think this would help us a little WRT the hypothetical carrier someone was just alluding to, and WRT the other hypothetical carrier also in the mix that only has like 400 pilots, it probably won't matter a whole heck of a lot anyway. A far, far more crucial variable will be when a merger happens. Right now we're eating a stagnation sandwich while others are in growth mode. Even a small carrier can pump out a few new hire classes and buff their over all relative list by a percentage that would take us years of epic hiring to match.
We need to merge now or wait until we're in unreal mass hiring mode and they are stagnant.