I’m not the OP, but I had wondered the same thing. After already seeing up the other *arr’s I couldn’t work out the point of Prowlarr.
Re your comment about resource constrained, I have just started using Sonarr and Radarr on a Pi4. They seem to work OK. Had installed but not set up Prowlarr yet. Hopefully that wouldn’t slow things down if I used it to sync the other apps.