That works, but you don't really need to avoid them. Even when I draw a healer, I just concentrate on killing the heavy damage-dealers. Interrupt Colossos's heals when you can, but I find that he's less interested in healing his friends than he is in healing himself, so I'll generally refuse to play his game, and just ignore his attempts to tank me 'til the rogue (and/or hunter) are down. While this fight, played straight, isn't usually ez-mode, I haven't wiped on it in ages.