Post Big Bang Holy Arrow question.

It's weaker than magic claw unless you are on a single target (pretty rare after BB) or you are up against a holy-weak monster.

Even then, training with heal should be faster than both other skills since it's just so fast and practical.

Pretty much this. Heal is better because it hits multiple targets, is affected by mastery now, and on top of that deals holy damage instead of heal damage. It's still only able to hit undead though, but most of your training spots will consist of that still. The one thing about Bishops is that their builds change, but not the dump skills. It's the same rules as before:
Don't max Energy Bolt
Don't max Holy Arrow
Don't max Doom
Don't max Mana Reflection
There will always be conflict of what to max, but the vast majority of Bishops will tell you the prior.