You sure you played Dragon Age Origins? It's very much possible.
It doesn't matter if there was ever healer classes in Mass Effect as the parallel I'm trying to make is that the issue people seem to have is entirely focused on the fact that you can't heal. As you said yourself, it's been proved in ME3 that a system which allows specific patterns to compensate for the lack of healing is something entirely possible. You say it's because Shepard is over-powered but, that's only your own interpretation of something which works just fine. Hence why, if you know a minimum what you're doing, victory is waiting for you.
As I said, give it a chance.
Lore reasons might be plenty but that will have to wait for us to discover that at release.
Yes, I have certainly played DAO many times. I play the most for story though in DA and don't like long fights, hence why I like lower difficulty compared to the Mass games. We will certainly have to wait and see, and I am hoping for the best.
To another poster who suggested not getting the game.... Never!
This is my favorite game franchise of all time, which is why my disappointment is so high that they've made these fundamental changes to character specializations and combat. What was so wrong with the system as it was before? Just slow down the combat of DA2, get rid of wave spawns and I would have been a super happy camper.
What's done is done now, I'm just really hoping this won't wreck my enjoyment of this otherwise amazing-looking game. I want to replay it dozens of times, so I am really wishing the combat mechanics will not annoy me enough for a rage-quit. 