How is keeping your relative seniority (within .5%) at the new combined carrier getting screwed? If you are at 50% on the NWA seniority list now... and 50% on the combined SL later... seems pretty fair to me. I think the NWA guys are letting their pride get in the way (i.e. I don't want to be junior to a DAL guy who got hired 1 or 2 years after me).
In my opinion, as long as the DAL guys directly in front of you/behind you (on the combined list) were at the 50% mark on DAL's list then it seems quite legitimate. Please explain why it should be otherwise.