The piece you are missing here is that everyone who is used to administering Classic Stream will need to become knowledgeable about how permissions and features work in SharePoint Online. If you do not currently administer or are not a content author using SharePoint Online, be sure to connect with your SharePoint Administrator or SME to learn or get their assistance in planning your new Stream portal.
It is absolutely still possible to create a "channel" in the new environment. The terminology is just different between Stream Classic and SharePoint.
If I am moving my videos for a channel to SharePoint, I will most likely either create a new site for the content to be stored in or else I will tag the videos with metadata in a library so that I can create a "channel" page that only displays videos that used to be in a channel. I can call that page by the exact same name as the old channel. I can even pull the content from that video library into another SharePoint Online website using a Highlighted Content web part. It is possible to create an online experience that is the same (or better) for end users in SharePoint Online as you currently have in Stream Classic.
Anyone can follow a SharePoint site just like you could follow a Stream Classic channel. Again. . . you are looking for a site instead of a "channel" but as an end user you would see the same videos if they are organized the same way on a SharePoint site.
The watchlist will be coming out very soon according to the Stream product team. They are aware of the discrepancy between the two systems and their top priority is to ensure parity between them as soon as possible. That functionality should begin rolling out at the end of January - so it will depend on how quickly your tenant receives this update.
If you need additional assistance, feel free to reach out to me directly.