So is how I'm understanding it correct?

With each 100 points of mastery your class increases a tier, giving you access to better stats and new abilities, but you can only get one of these new abilities immediately because you only get one perk point. Since the max mastery is 600, you only get 6 perk points that way. To actually be able to use all of the abilities in a tier with multiple, you would have to participate in special events or hunts to get additional perk points to spend.