the tags that Deemix gives you are usually pretty decent to start with
Indeed! Deemix also gets tags that OneTagger currently doesnt fetch (Composer, Label, Author etc.).
Genre (along with lyrics) are the tags that probably need most of the work. And because in OneTagger I'm using 3different platofroms (plus whatever deemix got) to fetch the genre tag, it can be a mess. Each platform may categorize songs differently and many times the program wont find a match for all platforms. I have to manually edit them all or create a bunch of different actions to automate this.
You can keep tagging files ~forever and still not have them perfect.. I just stop after when I think it's good enough and I might start tagging them again at another time.