There are multiple things to get confused: indexers and trackers.
Indexers are what people that don't have sonarr/radarr/etc interact with directly - a collection of magnets and/or .torrent files.
Trackers are what download clients interact with, usually magnet/.torrent has multiple trackers included in metadata. All these do is match hash to peers. You technically don't need it with DHT, but they speed up peer discovery by a lot compared to just DHT.
Indexers (really often just a forum) often act as trackers as well, but they don't have to.
Trackers often remove .torrent files and magnets at request, but leave enough information for you, you to create new magnet link and use their tracker for peer discovery.
The first few points you made are really great, this is often confused, but:
> Indexers (really often just a forum) often act as trackers as well, but they don't have to.
Indexers might operate a tracker (and often include their tracker by default in all their torrents/magnet links, but they're still not the same thing.
> Trackers often remove .torrent files and magnets at request, but leave enough information for you, you to create new magnet link and use their tracker for peer discovery.
Indexers are what people that don't have sonarr/radarr/etc interact with directly - a collection of magnets and/or .torrent files.
Trackers are what download clients interact with, usually magnet/.torrent has multiple trackers included in metadata. All these do is match hash to peers. You technically don't need it with DHT, but they speed up peer discovery by a lot compared to just DHT.
Indexers (really often just a forum) often act as trackers as well, but they don't have to.
Trackers often remove .torrent files and magnets at request, but leave enough information for you, you to create new magnet link and use their tracker for peer discovery.