I can sustain just over 2k hps for about 8 minutes, and then I'm generally out. Thats overkill for most fight, by far. So, I usually share the healing, and spend a fair bit of time dpsing. I do know that a whm can spam cure3 on a group and do over 3k hps, but they cannot sustain it. I'm not saying I beat every white mage, just most.

Galvanize isn't that hard to be efficient with, just use it before damage is taken. One of the "secrets" of dpsing as a healer, is understanding that you don't need a party with full health bars, they just need enough health to survive the next unavoidable mechanic. I'm happy to let Eos get to people in time, or I might help her out if I have a spare GCD, and all my dots are up.

The real factor to consider, when looking at hps, is over-heal percentage. I tend to run 30-40%, I'd be lower, but that Eos is overkill, and wastes a lot, but she can't help it (I'm usually 15-20% with Selene, but I don't get nearly as much dps time that way, and I end up more dependent on a healing partner than I'd like to be). Most white mages are 40-50%, given the nature of regen, that's understandable. Once in a while, I see an extremely efficient white mage, that can dps while giving me a run for my money on healing. Those are few and far between, but they are certainly out there.