Dr, I don't send out phract armies (too costly) but I regulary send out cav armies. 100k cav hit 500 abatis and I lose 200 cav or less. That's .2% loss. If you sent phracts the loss is even less.

If I send waves, the first wave of about 10k removes most of the abatis, and 40 waves of 2k afterwards take less than 50 losses (abatis don't all get destroyed in one attack).