PhantomGhost (I am BST but if I sit to regen mana, I don't do DPS... Main reason I disliked the setup).
In other words, the "inefficiency" wasn't the lack of a tank, but that you're a class that melees, leaving you little time to med. That problem is compounded by the "zero-downtime" chain-pulling hack-and-slash that the deep dives worsened.
As for needing mana to heal, most of the healing in my group was being done via mage bandages, during and post fight. You can't heal a single tank with bandages -- but when aggro is swapping between 3-4 pets, that means 3-4x the bandage healing.
PhantomGhost Having to let pets build agro because taking agro from them could be deadly without a healer
You don't need to let pets "build" aggro. You wait until one single pet gets off a taunt, period. Taunt is MAX_AGGRO+1. In a multi-pet group, that's usually within the first couple seconds of engagement. And if you rip aggro, you're not going to die -- not as long as you can root or kite. If you're in a dungeon fighting yellow and reds, the situation is a bit different, but not anywhere else.
What makes this comment ironic is that, even in a group with a tank, you should be required to let the tank build aggro. But the game deprecates aggro management, and every dps class believes it should start damage within 3 microseconds of the mob being engaged.