Thats odd, I never had to KoD attack my healers once my mage was placed, I was able to get my mage down before he showed up. (I needed to do this map 3 times to three star it due to a few issues I had with my team.) I did find I had to put down an additional lightning rod near the end as the KoD eventually managed to score two hits on my mage to kill him so I needed someone who could take a better beating once the KoD got closer. I used a valk for this.