Searching for files is not what Sonarr and Radarr are really strong in. They do an excellent job of managing files and keep track of shows. And occasionally ask an indexer to find them.

Indexers are what actually search files. Jackett was the popular manager, Prowlarr is the new hotness and really simplifies the process a lot.

But bigger point being Sonarr, Radarr, and Prowlarr work together to find and manage files. They are only as good as what you set them up to do. Prowlarr can search 50+ torrent websites for a file at the same time if you set up all the integrations for those. It is better than any one website because it can search them all, even RarBG when it was up. It also works with NZBs and search them all at once. Then you set Sonarr and Radarr to the quality and type you want and they'll pick from the search results automatically.