Please explain to me why a healer "MUST" be killable 1v1 because that to me makes no sense. In my opinion a healer should be equal to 1.5 - 2 dps. A dps should be able to put pressure on a healer but not be able to kill them alone. Yes I realize sorc healers are overturned at this point in time but that's not the point of the argument I'm making. And yes you absolutely can kill sorc healers 2v1. If you can't then it's either because A. You're bad, B. The other dps with you was bad, C. The healer was getting cross healed, or D. The healer had a tank.
I will reiterate, a healer should not be able to be killed by a single dps otherwise the role of a healer is worthless. However, a single dps should be able to put pressure on a healer forcing them to have to focus much more on themselves than the rest of their team. This is the case with 2/3 healing classes in Swtor right now.