I agree. I added my juvies at 5" to a tank with two 8" axolotls and really over the course of a couple months ive seen more bullying(no injuries) between the juvies, and nothing from my two older lol. Though the three juvies were together(apart from their cannibilistic stage) their whole lives.
Its really all about temperment of the actual axolotls I think. I do not recommend any smaller then 5-6" going in to a tank with a lotl bigger. I mean 5" and 3" maybe but not 3" and 10".
Ive heard of people never being able to take out the divider, but like I said ive had no problems. My two older ones are really lazy.. So maybe they just dont care? I seem to get lazy pets.. My rats are the laziest thing youll ever see. They literally pancake themselves and sleep like a pancake, all day.. Everyday. Except to eat and when i first get home/wake up