For me with characters that were far from min-maxed I'd say that roughly one in ten or more CC attempts actually worked. I had the dragon frozen once or twice, and knocked down perhaps three times in the whole fight and I didn't bother doing that to the minions, they focussed on my summons for the most part (as did the dragon). Watching a dragon stomp on a spider three times in a row and miss all three times kind of made up for the lack of CC.