I’ve never used the qBittorrent search function so if everything mentioned in my earlier comment is included in qBittorrent directly, then I don’t know. Use what works best for you. As I understand it, the main appeal of the *arr stack is that it does everything automatically and without you having to intervene to get what you want.
Correct me if I’m wrong, but I imagine that qBittorrent doesn’t automatically search for better versions of your media, automatically rename and move files to your specification, automatically evaluate search results to choose a download that matches your desired quality, automatically search for desired media when it is released (like new episodes of a currently running TV show), automatically import subtitle files or extras to your library, or automatically grab metadata for all your media.
I can’t find it now, but there was that one text post that went something like “1. Copying a movie costs the studio money, 2. Download a movie, 3. Make 1000 copies, 4. Studio goes bankrupt”