Nice idea!
After a few more attempts in creating several heroes and understanding the system better, I must say I panicked about the cost a bit too early. I played my first game yesterday with two custom made heroes and it was great fun and balanced. Like your example, it's actually amazing to get a support character in your army, where I was first focussing to much on damage output and survivability.
This is the "Child of Light" I used for my Realmlord's army yesterday. (18DP / 180 points)