Shadowverse

Why is the "Roach Bolt" ability better than just a regular "Roach"? In round 7, I brought the enemy down to 4 HP with three Roaches. In round 8, I survived thanks to the Queen. And in round 9... you can see for yourself. Although, maybe if I didn't have the "Roach Bolt," I would have saved the Roaches for a combo. Also, I got very lucky that it killed Khavy on an empty space, and instead of sending a second Khavy after my Queen, Nefitka sent Urd and Din-Don, and I had to trade a Lich for her.