Sonarr and Radarr are there for managing your requests, so they’ll handle things like downloading it when it’s available (either because it’s a new release or because the torrent/nzb weren’t readily available at the time you added it), upgrading an existing file to a higher quality version if it becomes available, sourcing a new copy if you mark the one it found as bad (e.g. huge, hard-coded Korean subtitles ruining your movie).
If you’re trying to find new stuff based on vague conditions (like “90s action movie), I don’t think any of the self hosted apps are a huge help. You’re probably better off sourcing ideas from an external site like IMDb or tvdb (maybe even Rotten Tomatoes?). Those sites maintain their own rich indexes of content and tags, whereas the self hosted stuff seems to be built more around the “I’ll make an api request once I know what you’re looking for”, which sucks when you don’t really know what you’re looking for.
I think there are even browser extensions for IMDb that will add a button to the IMDb movie page letting you automatically add it to Radarr if you like the look of it.