One problem is not only the bad damage ratio but also the fact that they have a long recast delay. But by far the biggest problem with this line of spells is that they are few and far between. For example strike is totally useless around level 6 or so, smite becomes useless in the low 20s, and wrath is totally useless by around level 40. That having been said you will still be glad to have these spells as they do allow you to stand some kind of a chance against your foes and also are great for cleaning up running prey. One other glaring weakness in the cleric line of spells is the lack of utility spells.
Clerics basically have two utility spells at their disposal.
The first is the reckless strength line of spells. These spells are somewhat useful but they pale in comparison the a shamans spells. The second is the invigore line of spells which restore a players stamina. While this is useful you rarely have the extra mana to spend in a battle on restoring ones stamina. Now let's assume your convinced that you want to be a cleric.