You guys are doing it wrong and Sten is a good character due to his damage potential and innate durability as a warrior. I'm going to be blunt: the MMO conceit is a crock and leads only to failure in my Dragon Age experience. I know this in part because I play tons of MMOs and this game, if anything, plays out like an untankable encounter in which everyone is responsible for their own health, not a tank and spank. Just bear with me for a moment and I'll explain my admittedly unorthodox viewpoint.
MMOs work the way they do because of a few unique design decisions that simply don't apply to Dragon Age. MMOs emphasize the Tank and Spank because you're typically worried about one overwhelming foe per tank, each of whom will cheerfully annihilate anyone but a tank within the space of a few swings. The gap between the tank and everyone else in the survivability sweepstakes goes beyond profound, but even he takes immense damage and requires a full time healer to survive. To counter this, healers in MMOs are supercharged health throughput machines that can take a tank from low to full in the span of a few seconds, and can massively overheal anyone else. This means that using heals on anyone but a tank is "wasteful," since healers are restrained by mana costs, not cooldowns. It's a black and white world: healers heal the tank, tank takes the damage; any variation and you start losing people.
Dragon Age isn't like that; hell, strategy wise it's almost like a party based Diablo you can pause. Enemies attack in number and when you die it's usually because your dumb ass was surrounded again. No class can chain cast super powered heals, yet the few healing spells available are remarkably inexpensive, so you're fighting to keep people alive until Heal is available again rather than worrying about your mana pool. Armor is helpful, but not as helpful as hitpoints. And most important of all: All the classes are hybrids and all of them can have decent but not overwhelming survivability. The key to not letting characters with low con die is to boost their con.
A character like Alistair can take more damage and handle flanking enemies better than the other characters. That doesn't make it a good idea to let 4 enemies pound on him at once. Keep it to two or three enemies attacking any one character whenever possible. If it gets to be more than that you need to shift priorities to taking one of the bullies out of the fight ASAP before someone gets cut to ribbons. And don't be afraid to let your mages take a few hits. Trust me, they can take it if you build them right; Morrigan has enough baseline strength to wear decent tier leathers if you're paranoid, and even without them she can often take care of herself by using Vulnerability Hex+Drain life combos. Letting the damage get spread around won't kill you; in fact, it just makes it more manageable. Ending the battle with everyone at half health is better than ending a battle with an injured Alistair and everyone else untouched. If you must use abilities like Threaten, make sure you have at least two warriors using Threaten together so the incoming damage is split into manageable chunks.
