I'd bet the "get focused and die before you can get a heal off" scenario accounts for less than 5% of your time in a warzone. I'd also bet the "No one is chasing me, nor am I taking damage" scenario is also less than 5% of your time in a warzone.
The remaining 90%+ time is all time where you're taking damage, running from guys, having them peeled by allies, getting heals from other healers, etc. You can't say that HP has no merit in this situation.
You guys can feel free to pretend that it's black-or-white, all-or-nothing. Azaranth has done some legwork setting up some profiles, providing mathmatical evidence, and generally backs up his point of view with facts. You guys should try and do the same.