Hm, might be worth checking out. Haven't played in a while but iirc, Prayer synergises Meditation so you'd get effectively double Prayer. On the other hand, if you do not use the insight polearm you'd only have half the regen you are used to.
I have to admit I never tested this but I have always been happy with my defiant mercs performance.
Belated replay to ndt: I would recommend pretty much the same allocation as for twinked play. Roughly 100 Str / 200 Dex / rest in Vit. With that you'll be able to use most bows, javelins and armour while having a good HP pool.