You must be really be bad at PvP-ing. If your Holy Light spam is so bad, I wouldn't even take the effort to switch to Gtb, that renders Stave useless. You need to be able to force someone to use Gtb, but with a pathetic spam rate, it's highly unlikely. What I just said was they made a valk for Priest to be PvP able, what's the point of having the weapon if you can't use it to its potential? You mention that the only use for a Priest is to just buff and heal, but if that is their only sole purpose, can you explain to me why did they created Eir's? The answer is quite obvious.
And you said Priest have Holy Light and Stave, so their spam is fine? What you are saying is that, they have this two skills, so there is nothing wrong with the spam rate. It's just the skill they have, nothing relate to the spam rate.