What in particular do they hate about twitch and what type of streamers are they? (top, emerging, casual, etc).

I too hear a lot of complaints about Twitch too but I feel that most of them have nothing to do with the product, but the zero-sum and competitive nature of gaming streaming. It's just difficult to succeed as a gaming streamer (or content creator more generally) and the vast majority of people who try will never make any meaningful amounts of money, so frustrations tend to be attributed to the arbitrary quirks of the platform, even though that's just the nature of any content business.