Cleric is at least a part fighter at heart.
Warpriest is half cleric half fighter.
The combo would be ~70% cleric, 30% fighter.
I think you need to start with: what do you want from this class? A divine fighter with 9th level spell casting? Well, that's basically going to be all you get.
It doesn’t need a power boost, but its class features could stand to be more interesting or dynamic. Newer classes’ features are more “fun”. You could say a wizard has the same issue, but the wizard’s spell list is much more diverse.
I'd prefer playing an oracle for that reason, Ciaran. Trying to mix warpriest and cleric doesn't seem likely to get you there though. Maybe if you could trade something for channeling feats - maybe medium armor for one such, or diminished spellccasting for several - you'd get something distinct to the cleric and more "fun".
Why are you trying to boost the Cleric? They're already top of the heap.
Strongest thing the Warpriest has to offer the Cleric is the one real benefit it has over them. Fervor, for swift action self-buffing.
Yeah... I'm rather curious myself as to what you were looking for, especially since cleric is one of the most powerful classes in the game as is...
I'd assume one of two reasons for thig
1: he feels cleric is 'boring'
2: they've had some horrible experience where every cleric they played was awful so he seriously thinks they need a buff (or experienced this situation as a GM