View them as large chariots that are far less likely to die. The trick is to hammer home the charge and then quickly utilise the shockwave using cavalry/infantry. I find in vanilla war elephants are very very hard to kill. But usually when you start to lose them, you'll quickly find the entire unit has paniced and will need to be killed. Oh and one final thing... keep them away from onagers. A single firepot can kill four and panic the entire unit!