Splitting the tag may be a good idea, but not between female domination and femdom, since the latter is literally identical to the former: female domination [its just a combo of the first syllables], and they mean the exact same thing. Plus as long as people are keen on using terms as they see fit, that would only increase confusion.
Female domination/femdom should be reserved to what it actually means, adding a modifier in front such as soft-femdom and hard-femdom would be more a useful tag separation. Or in case of really barely even femdom, something like "fem-top" would be better, with femdom reserved to actual femdom content.
That being said, I am more in favor of people using words correctly, nothing is stopping devs except perhaps ignorance in some cases to add a modifier in front of their tags: soft/hard, light/heavy, mild/extreme, etc, or even specify that a given tag only refers to 1 scene: femdom (one scene), etc.
During my time on this site I learned my way around. For example if a game has too many tags [and its all brewed into the same narrative, without splitting paths], some of which are opposites such as femdom/maledom, and also have tags usually not associated with femdom play such as "vaginal sex", "harem", "loli", etc...then you can be sure that the female domination tag, if its among them, only refers to some feather-weight kind, maybe limited to one or two scenes at that. This combined with the game description, preview-pics, and the number of likes, almost never makes me fail in predicting the actual nature of the content.