I disagree with you on this one. Feral spec'ed druids can heal. Though its obvious that they will never match restoration druids, and I doubt i will ever heal in a raid situation without respecing, when i heal five man instances, I do just fine. I often have 3k more mana then priest, and almost never run out of it. My only problem is dealing with burst damage. The extra healing from nurturing instinct helps with that (i'm assuming its about 200 or so spellpower on healing spells at 260 agility, but I don't know if it helps enough for me to keep it. Anyway, because it is so ignored, I've been experimenting with makeing it more viable.
One thing I know from experience is, for doing five mans, Bears heal just fine, if you measure success in completing the instance efficiently. further, being able to fill all three slots in a five man, allows me to get into parties very quickly which is always a plus for trying to gear up. When I get into more hardcore stuff like endgame content, well, then I agree I will have to spec the branch for the job.
I am missing the earlier iterations of the game though, were all armor didn't look the same, and druids didn't seem to be cornered to spec for only one narrow purpose. but that's a topic for a different post.