I tested them in a quite long game, and chaff gets crushed by W9, F4, N4. True they tire quickly, but they are easily replaced.
Edit : forgot to admit morale 7 on many commanders is a pain in the but.
All in all it is not my favored faction, but I wouldn't rank them the lowest position, because of recruitable everywhere sacreds, which makes for pretty efficient early games(I've reached astonishing rates with them, as with any other sacred oriented faction)on which you can capitalize, and efficient magic, even if they are crippled by somewhat heavy flaws.
In fact it is hard to say which is the worse, but personally I hate the animal tag, for the reasons listed above and the dreaded animal awe.