Seniority lists are a bad thing as they reduce terms and conditions for all, including in the companies with the lists.
Dunno where you get that idea from, real life experience suggests otherwise actually. The airlines that are currently mainly lowering T&Cs are actually those that do not have a seniority system. Working in a seniority airline we just raised our pay by so high an amount that we are not allowed to talk about it anymore as it is in serious double digit percentages per year for the next three years.