I agree on the subconcious attack it gives your opponent. I mostly use them for interior enfilade attacks. I normally only have the one infantry brigade and one calvary brigade and put dragon ogres and hounds etc inside between the brigades. When close enough the dragon ogres can usually sucker the oppnont into a game winning flank attack with the massive hit count they bring. 8 per base in the open, nearly twice that of a chariot.
But yes, they are expensive and i wouldnt use them in a small battle.