I haven't read through this post in detail, but I m going to shortly and will probably have more comments, but I wanted to offer a small criticism.
Killing healers is very important and has a very high priority, but it's not always as high a priority as a lot of people think. It's priority goes down the more organized your team is relative to the other team. If you have 3 - and especially 4 - DPS trying to burn down a single target, it doesn't matter how good a healer is, he's going to die. Now, if the other team is organized enough to swap guard to a focused player and have two healers keeping him up, then you need to worry about the healers. When you're in a pug or something, though, those healers will probably need to go because it's really just one or at most two DPS on a given target and a healer can keep him up.
Now this is all really just background to my main point, which is that in certain situations targets other than healers can have higher priority - namely, DPS. If you're on offense on Voidstar, the healers should probably go first. However, if you're on defense on Voidstar and the other team has good DPS, you'd better darn well be focusing that DPS down or you're going to wipe and give up the door.
Again, it's all situational and dependent on the respective teams' levels of coordination.
I agree that there might be certain situations where killing the healers first might not be the best idea. However, I have an example that might illustrate this point pretty well from Novare Coast:
When fighting over the southern turret, which is situated on top of a hill, I will actually plant myself (gunslinger) right next to their healer and use my knockback to throw them all the way to the bottom of the hill. If I'm feeling especially generous, I will then throw a flash grenade on him and if he breaks that, legshot. This does two things: 1) he can't heal anyone but himself when he's down there, and 2) it separates him from his tank, rendering guard useless.
While the healer is stuck waiting at the bottom of the hill, the rest of the team can focus down targets with ease.
This is a great basic list of priorities that every new player should read since it should only take 5 minutes. Too bad many players are too selfish and will always just go for kills regardless.But for those of us that actually like to win...