I’m also willing to throw PW:Shield in the mix for ‘too good not to include in 95% of Priest decks’.
Well it is correct as well, the reason I do not see it as main problem is it would allow priest to play some of the weaker cards. a 2 mana 3/2 boosted by PW:shield becomes a good 3 mana drop while also costing just 1 card. It allows priest to play some of more obscure but good control cards while not losing draw advantage.
It is problematic but makes few cards which aren't welcome in other control decks viable in priest like pyromancer, ooze etc.
Losing it would limit priests possible card pool as some cards are just meh on their own but a 2 hp buff makes them usable while losing cleric would not affect other cards. Injured blade master would still be playable, as would injured tol'vir. On the other hand pyromancer without card activator for cheap or lightwarden become cards too easily removed otherwise.