Mixer had potential as a streaming platform, they completely failed to create a culture anything like what Twitch has. Any streamer who wanted to move to Mixer would have to sacrifice being part of that Twitch community.
Their culture though... Before Shroud and Ninja joined, there were rules that you couldn't tell people your age. They had rules on how wide your shirt straps could be, and just generally seemed like if you had any opinions on other people, you would be chastised. They valued explicit political correctness, but that's not so good when you're making a place designed for just chilling and hanging out... At least, not when you're trying to grow.
Another way to word it is that the online gaming community is extremely toxic and you have to accept a decent chunk of that toxicity to grow a community in the gaming space.
Put in another way: each stream is an individual community. By making such explicit rules, they are policing culture and suppressing certain identities. That is counter to the environment needed for growth.
If a stream and its viewers is a community, then on Mixer you didn't really have the chance to make that community "yours" -- rather, you had to be what Mixer wanted you to be, which is some made-up archetype of the advertiser-friendly hip gamer who captures that coveted market segment without saying anything even remotely controversial.
This sounds like FUD. The streamer controls the video encode, not the platform. Also Twitch has had <1s latency streaming for more than a year.