No, that's the whole point of PeerTube. PeerTube scales up by spreading the playout load amongst everyone who is watching at the moment. If a thousand people are watching your video, most of them are getting the content from the cache of others who are also watching at the moment. Not from the hosting server.

This works well only if many of the watchers have significant upload bandwidth and aren't behind firewalls that prevent them from outputting blocks of video.

This is different from torrent-type systems or Usenet, which distribute persistent copies. With Peertube, only the original server permanently hosts the video. Everybody else is just caching. So the disk usage of watchers isn't that big.

It's all done in the browser.

That's why it's built on WebTorrent, to share the load across users and instances.

There are cdns that can help..