> But then I eventually understood that you're talking about latency between viewers

The latency between streamer and viewer on Twitch (in low-latency mode, which is the default) is normally less than 5 seconds and often between 1 and 2 seconds. The player actually slightly speeds up the video if it exceeds 5 seconds.

This is essential for interactivity, because the streamer can ask a question and get a response without constant awkward pauses.