What I seen so far is that the change has pretty much broken the healing function of the companion. Here is a case I even shared it in general chat in game. I had a group of 4 mobs, 3 were dead, one still CC'ed. My dps Sorceress was at 53% health..... and guess what, no heals. The companion was set to heal, I never changed it to any other role.
There is another issue, I can have all the mobs on me, and yet I get no heals at all..... why it is busy healing herself for no bloody reason... so I die no heals. In both examples, the affection is 13.
The companions of 4.0 were just fine. I tried soloing World Bosses to see if the complainers were right, but get squashed like bug (as it should be), drag large numbers of mobs to me (never did they go to the healer) sometimes it did not go so well. Gaming life in general....