I don’t think it should do that automatically. I have artists who recorded, say, Indie Rock albums and Alt-Country albums, so the artist is tagged with both. But that doesn’t mean that their Alt-Country albums should be auto-tagged as Indie Rock or their Indie Rock albums as Alt-Country.
Edit: Or to stay in the genre
I don’t want Carcass‘s Grindcore albums tagged Death Metal and their Death Metal albums tagged Grindcore just because the artist has both tags.
But it’s true that genres are very inconsistent. As to your problem, are you aware that you can multi-select albums and edit all of them at once, like select all albums by an artist and add/remove a genre to/from them?
Edit: I detailed multi-selection here for playlists but it applies everywhere: