HACK is talented. They aren't the force they used to be, but when you collect a group of friends who worked hard and enjoy themselves for years and years, experience can get you pretty far.
I don't necessarily think making it to the quarter finals is a testament to "Oh HACK is super strong" so much as it is that most of Toribash is tremendously weak, and that many matches in Clan League will only keep those latter clans in long enough to face one of the few real powerhouses. When I look at the bracket, I see 3 favorites, 2 clans on the outskirts of favorites, and beyond that it becomes farfetched.
I think if Frost is serious and spend a day as a clan going over some E-sport thought processes they could at least beat HACK, sure. Probably won't happen unless they do that though.