Personally I think an even more broad form of the tag should exist (which even could have further justification for its existence). If there was a general word for these shounen/Isekai/reincarnation/harem stories I think that would better encapsulate the real sort of tag that is needed?
You can search by shounen+Isekai but not all of these stories are actually Isekai and there are a lotttt of stories I would still catagorize as "written for knave/general audiences" under the shounen tag. They're all technically shounen as well, but I think when people look for a shounen story they're looking for something action/loud. Say, something you'd expect out of a shounen magazine, like you'd expect something romance oriented with fluffy humor from like magazines under the shoujo tag.
The slavery genre is something I would say has spurned out of a larger new-age shounen, which I think is of a different genre then standard Japanese bruise-coated shounen manga that a lot of us has grown up with. A slavery tag would be nice but I think a lot of these webtoons and manga could be better united under a tag between shounen and seinen? Unpopular opinion though, probably.
