Lame spells? Cleric spells are quite good. They don't get the flashy stuff, but They do get something from everything. They can not only destroy, but also heal.
They can reduce all but the most hardy warriors to a broken wreck with one spell. They can resurrect the dead. They can cure almost everything. They can protect from evil (or whatever they happen to be opposed to). And they can turn themselves into fighting machines that put warriors to shame.
Of course, you don't get all of this right away, but that's because an acolyte doesn't have the same "capacity" as a high priest.
The power of the spells granted to you doesn't depend on the deity, it depends on the caster. The more experience they have, the more conviction and dedication, the richer the divine rewards.
As for turning undead: It works well to obliterate hordes of soldier-type undead (low-level zombies and skeletons) without endangering anyone (sure, you could also torch them with a fireball, but then you'd have roasted townspoeple all over the place)
Against stronger creatures, it can also work, as it takes their ability to act freely. That way, even weaker defenders (like town guards) can attack them with impunity.
Clerics aren't divine artillery, and neither are they supposed to be divine artillery. They're champions, sure, but also protectors and defenders.