I beleive Avatar is a summoning spell that creates, essentially, a golem of your God's power. In which Bile's stinks.
Sure, it has the usual HP and Attack of an Avatar, but it has NO DEFENCE, which means it can be killed easily.....Unlike Brigid's Avatar which has 1000 HP and 50 attack and defence.....and Brigid's easy ressurections. The only major porblem is, well, the dependance on others for frikkin food.