Before dual spec I would be able to heal fairly decently as prot in my holy gear, I couldn't main heal a raid and didn't try even a 5 man but was a good off healer. I bet if you played with it enough you could produce a decent hybrid build that maximized survivability while still having acceptable healing. If you have 3 going they don't all need to be awesome. The biggest thing is getting a decent mana pool as prot and that is just getting gear with Int on it.