I'm not sure why we're basing everything off HP anyway, more HP just implies another tier of gear, though often the lower tier re-itemized to have great secondary stats is better than the off-the-shelf higher tier pieces.
I agree that HP is basic indicator of players gear level. But it can not be used to determine players strength. As a sage healer, when I hit 50, I had ~12k HP. With ~14k HP I started doing operations. Now I have ~20k HP and I do not need any more. Nothing can one shot me in EC HM, and everything else can be healed.
I remember HM FP runs with 16k HP tanks and 13k DPS. It was harder, but doable with a bit of planning ahead. You need more HP only if you want wild brainless rush through FP.