This is a case of rose tinted glasses. With one notable exception that was eventually rolled back (Nanamo's assassination) the politics OP describes in ARR was mainly set dressing. You need to have a generous interpretation of ARR and a very ungenerous interpretation of DT to make three claims. For example,
This is just flat out not how that went down.Garlemald is destroyed offscreen and then we - who killed hundreds or maybe thousands of their fathers, brothers, husbands, and sons - waltz in and pass out bowls of soup and now everyone is sociable, with only a few "disgruntled" people, let alone anyone trying to assassinate the enemy's great hero and the scourge of Garlemald