Yeah, threaded conversations based on replying to comments and sorted by a recency/popularity algo are less usable, in some ways. But the forum format of sorting everything by most recent reply and only being able to append to the end of a conversation has it's own issues. So I don't think one is worse than the other, it's more like the difference between how threading and replies work on email vs. IM, they each have their uses and their drawbacks.