by having larger aircraft pay more it offers opportunities for pilots to decide if they want to stay on a smaller aircraft and enjoy better relative seniority or bid larger aircraft and earn more money. Pay banding all aircraft together takes away both those choices.

let’s take a hypothetical ATL captain. Let’s assume they are about 6000 system wide. Currently this pilot has the option to bid 717A and be in the top half of their seniority list and get days off that work for them, conversely they could bid the 7ER and give up the schedule control in exchange for a raise. Some might pick the 717 and others the ER, but current that is a choice they can make. If they were pay banded both those options would go away. The pilot who is willing to make less for better relative seniority is no longer able to do so and the pilot who wants to earn more now has no where to bid to do so.