Hp pool for Hard Mode Titan

Currently I have almost full Ampdor Keep gear (Item lvl60) with a few pieces of darklight thrown in but it seems the hp pool needed for hard mode titan is far too high. With my current gear I have 3162 hp but 3500 appears the be the minimum, especially when it comes to being invited to a group.

How can white mages get a high enough level of hp without stacking vitality materia (which are incredibly costly on my server). It seems the only option is to have a superior gear level compared to everyone else to compensate?

Get more darklight gear? I think you should really have at least 4 pieces including 1 main piece (non accessory). I was able to do it with Ifrit weapon and 4 darklight rest was AK gear.

3162 is enough for Titan, but of course having more doesn't hurt. HP isn't a requirement so much as it is avoiding unnecessary damage. The only thing people "ideally" should be getting hit by are the stomps, and in order to counteract the healers need to start casting their Medicas/Succors before the stomps start.

To be honest though, it won't matter how much HP you have if you're not pre-emptively casting heals on everyone for the Stomps.