How gear-dependent is holy priest?
I'll usually run 110 content with a heroic-geared druid or shammy, and I feel entirely comfortable being healed by those; however, I helped out a levelling 107 guildie holy priest in a Normal Eye of Azshara, and was very uncomfortable with how my health was spiking; as a prot paladin, I outhealed him, and I'm not sure that's how it ought to have been with the setup we have.
There are two caveats; one, prior to this expansion the priest was Disc, but he's decided Legion Disc isn't really suiting him, so he's trying to turn his skills to holy - so to some extent there's some relearning going on. And secondly, he hasn't actually gained much gear while levelling; he's still in a five-set from HFC, he's still using the legendary ring (which, IIRC, starts to peter out in usefulness about 107ish?); his equipped item level is 740, and that's including the 800 waist he got from when we completed that EoA.
I suspect I need to gently prod him towards not ignoring quest rewards, no matter how tasty that set bonus might be