You have a few options, there are two plugins here:
- Move "feat." from artist names to album and track titles. Match is case insensitive.
- Removes feat. artists from track titles. Substitution is case insensitive.
Or you can use %albumartist% which will usually only contain the 'main' artist you're looking for.
However 'album artist' is already set by Picard, so personally I would keep the 'artist' tag as well (feat. and all), but arrange your library by album artist instead. Any decent music player should have that option, and then you don't have to water down your tags