I hate how Twitch puts over a minute of pre-roll ads before you can start watching a stream. They should at least wait 60 seconds, I can't imagine how many people have chosen not to catch a new stream because they'd immediately have to sit through over a minute of ads before even getting to any content.
All things considered though, I think you are right that the option that forces it at the beginning of the stream is obnoxious and affects the interest of those intending to stream. There's likely a better way (similar to your suggestion) that gets people involved in the stream first.