This will take some heat but in my mind the only fair seniority merger between two National/Majors and one regional is this: % based merger between F9 and Midwest including all furloughees and then staple the RAH pilots to the bottom. Then place a 5 year fence on top. Or Merge F9 and Midwest and keep RAH separate much like Alaska/Horizon.
IMO, Major airline pilots carry more career weight than the regional pilots do. I know the RAH pilots won’t like this but if it goes before an arbitrator you can guarantee that they will take that into account. Bottom line, no matter how you cut it is that the regionals are a stepping stone to the majors so no regional pilot should be spring boarded on top of those who have already done their time.