The way MusicBrainz defines a work is rather at odds with how users consider tend to use a work.

Consider iTunes for example their work and movement fields are clearly considering a work to contain multiple movements and is aimed at 'classical' music.

Users who are interested in a work field for the purposes of tagging use them for grouping movement in works. They are not interested in Pop songs that have a part of relationship to a work that is not part of a larger work.

I would ask Picard developers to consider using the same field that Songkong does for MusicBrainz works rather than using the WORK field. I struggled to find good name but SongKong uses MUSICBRAINZ_WORK_COMPOSITION for the work that recording is directly linked to and MUSICBRAINZ_WORK for the top level work that you end up with after traversing PART_OF relationships from the MUSICBRAINZ_WORK_COMPOSITION to another Work, and so on. If a recording is linked to just one level of work then MUSICBRAINZ_WORK_COMPOSITION and MUSICBRAINZ_WORK have same value.

Then only (if you want) to populate WORK if the MusicBrainz recording does link to a multilevel work, this links in with PICARD-1043 since there is little point adding support for Movement if you don't set work so that it corresponds with Movement.