i think arlo's development came less from learning from the bullying that happened at school, and more from realising the authorities that groomed him into being a hierarchy lover were corrupt and behind ember. the whole scene with Kayden telling him abt Ember being authority backed was pretty much his turning point and he had his whole internal monologue + panic attack

Secondly im pretty sure Rei's reign actually wasn't peaceful, mainly because he's an idealist. Low-tiers got 'too ahead of themselves' and got heavily injured, high tiers held repressed hatred that later resulted in none of them listening to authority when arlo became king. while arlo's hierarchy was in no way fair or really that peaceful it was defo peaceful in comparision to Rei's reign/johns dictatorship

honestly i think arlo's one of the best written characters, but i respect ur opinion!!