LIke someone mentioned above, the problem lies in how everyone is setting that tactic. The tank needs to be set up to defend itself. Ill explain an avg fight for my group. Im playing on hard rather than nightmare on my first playthrough, and I hardly even take damage on most fights. I play with me as an assassin rogue, Cassandra as the tank, Solos as the Mage, and I play around with the other spot. Vivan, Dorrian, and Sera. I tried bull, but once you get him deep into Reaver, hes too hard to manage without playing as him fully.
Cassandra is set to defend Cassandra. Solos Defends Cassandra. Then I follow Casandra, and the other DPS follows me. I start every fight in tactics mode. I send cassandra in with shield bash to the middle of the fight, or too any shielded enemy. If they are bunched up, I have soloas use the rift pull shrinking circle move(name escapes me), and drop a mine in the middle. My rogue kills the softer ranged DPS with me controlling. If I have a mage, I set up a shatter combo for a two hit kill with a stealthed, flanked, twin fang shatter combo. From there I mostly just let the AI do its thing. Solos never even comes into melee. Viviane follows me around. If Sera, i double click to hold position, but I like Viviene. She doesnt do as much damage, but I dont have to manage her. Shes near unkillable with mage knight, a smidge of frost, and deep right side spirit. Cassandra is set up to maximize guard through here gear and build, so she seriously never dies. I only click on her when i want to use that final templar demon explosion.
For longer fights Ill micromanage a bit to get the most use of solos, but my rogue does so much damage as an assassin, its not an issue. I imagine on nightmare I would have to do more. I also set all AOE ai to off so I can control when its used. I do the same with Winters grasp to control my shatter combos.
Also, make sure all your mages take the spirit ability to reduce aggro. You end up having more ability points than you need as you dont have enough spots for abilities, and even if you did, you wouldnt have enough mana.