I just played in a random party.
We killed him in less than a minute, corner tactic.
While staying in that corner made it very easy to kill mobs, here and there a mega combo succeded.

After that I joined groups and I constantly keep dying cause we can't time the combo so the boss runs to one of the towers and heals himself -.-
Having mobs hitting u while persueing the boss is not only disturbing, it splits up ur group and makes it really hard to combo.

One thing I don't understand...
The time we could beat him we didn't use auto-attack at all, but why?