Nobody seems to worry about new hires with much more experience than the guys they are flying with going to the bottom of the seniority list at their carrier. I had 18 years of experience when I was hired, still went right to the back seat. Flew with plenty of folks who had less experience than me. Didn't make me any more senior, nor should it have.
If we are going to have a seniority based system and a new airline is created, there are going to be folks who don't get the benefit of their years of experience. That is the way it is, deal with it or go sell insurance.