Each activity that grants a Powerful or Pinnacle reward will only grant that reward to the first character of a class you complete it with. Bungie fixed the exploit of powerleveling using the same character class multiple times early on in Destiny 2's lifecycle. If you complete an activity with a character of the same class as another character that already completed it, you'll receive a normal reward. If you completed the activity on one Hunter already and then did it on a second Hunter, the second Hunter would get a normal reward. You're missing out on rewards because you're using 3 Hunters.