Let me be absolutely clear, VIT > STR up to a certain point. Once you can survive
reliably, any extra HP you can achieve won't make that much of a difference in your tanking capability. I'll concede that there may be situations in the current end-game content where enough of an HP buffer
may allow healers to DPS, but asking your healers to DPS can, and often will, be very risky. But, really, healer DPS comes down more to player skill and incoming damage frequency, rather than "500 more HP" on the tank.