It is a straight fleet replacement. Seniority doesn’t apply in that case. If you go by your reasoning then any captain behind you on the seniority list should be demoted immediately and you should get their spot regardless of fleet etc. It just doesn’t work like that!!
Well that all depends on the rules of engagement. The 737 replaced the EJet and those guys got demoted because they didn't have the seniority to remain in base.
This whole thing will become unhinged if VARA loses the Rio contract and a bunch of F100 Captains become BNE 737 Captains.