I have been using them behind my comitatensis/spears line with flanking cav and mayber one or two missle behind-more to mop up roaming horse archers than any offensive role.

You do make a good point kekvitirae in terms of the subtlety of their usefulness. I am playing my campaign on H/H and find that their chanting may very well be giving me the added morale boost during the battle climax.
The comitatensis are rather tough to begin with but paired with the chanting they are even meaner than usual and seem to resist envelopment better.

Still, a strat map convesion effect would be more redeeming.