> your stream can’t be lower quality than what you send to other platforms

Twitch just passes through the stream you provide without transcoding at the top quality level. They only transcode for resolutions lower than you are providing (and ration those transcoding services).

YouTube always transcodes, even if the resolution/bitrate you are streaming is suitable for viewers, slightly lowering quality.

Therefore unless you are providing a lower resolution or bitrate stream to Twitch yourself, you can never fall foul of this. YouTube will always lower the quality from what you provide.

The "no-combining activity" is a direct shot at Restream.io etc which provide unified chat streams.