They are still useful. You just have to remember to drop rocks before you charge. Also, you have to remember to face them the correct direction when they land as they do not have 360 LOS anymore. Otherwise, you cannot charge the enemy you dropped rocks on (or another if that wasn't your choice).
With all the nerfing they got, the biggest thing that offsets that is the stomp special rule. This additional hit is amazing. My skink cheif on a terradon (equiped with fencing blades-WS-10, 2x attacks) + stomp killed a Vampire Count in the first round of combat. Amazing results.