No seniority in easy.... Since all join with wildly different experience (from 200 hours to 20000 hours) then I don't think it would really work anyway. We also don't bid for routes or flights.
Since we work 6 and 3 (sort of when things get better) then you are allocated a group within which you bid for leave. As for promotion - seniority or no seniority list, if the airline stops growing there is a halt to promotion. They do use date of joining for some things (eg base transfer requests) and no doubt if there was a halt to promotion this would come into play somewhere as well.
I think DBA may well continue to operate as a separate part of easy (just as EJ Swiss does) so I doubt you will be overtaken with hoards of pilots jumping in front of you. Perhaps a few Belgiums trying to get closer to home.....
Sorry you didn't get more answers but we are all working too hard...............:o