I know exactly how you feel. After my first run of Stone Vigil, I was thinking I was completely useless as a healer and was about ready to give up, too. But now I realize we just had an undergeared gung-ho tank, and that combination is going to lead to inevitable wipes.

The mobs in Stone Vigil are harder than the bosses. It's important to take it slow and watch out for those patrols. The tank should be grabbing the patrols and pulling back so you can fight them 1 or 2 at a time. If you go rushing in, you'll end up fighting 4/5/6 enemies at a time, and you'll have a bad day. The last room before the final boss has 4 dragons in it. The treasure in the room is always junk and not worth it. Just skip it.

When I've done it with tanks I know, who take a slow and methodical approach to pulling, we've done it with little trouble.

As for the red circles and other enemy AOE, just get out immediately. Don't wait for your heal or whatever you're doing to finish, just run and cancel it and get out. The tank/dps will just have to survive those couple seconds until you can get off a clean heal.