I just did it again and this time was no problem. It seems like each group was about 2-3 mobs, so he'd do them one at a time. The last time with the issue the guy had probably 3 or 4 groups in total so was like 10 or so mobs. This time was no problem was even able to do Holy a bunch. Have to say I really like Assize, especially right before the final boss when there's like 20 of those dragons that come out all at once. I popped CS then Assize and I took them all out in one shot lol, that was pretty satisfying.