This sounds like a bug – I just edited the tags for an album in my library and the changes showed up within a few seconds, no rescan needed. There are some configurations where “real time scanning” can be less reliable, but forcing a rescan (of either the album or the folder) should work. If you can give us steps and a rundown of your setup, we can try and reproduce this.
As for the question on the genres, I understand what you’re looking for, and I don’t think your request is unreasonable. But the system is set up this way because we have a responsibility to support hundreds (or thousands) of genres, and in many cases that involves people who want to mix genres from their file tags with Roon’s comprehensive genre hierarchy.
So the system needs to work for everyone, which means sensible defaults and the ability to edit your genres however you want. A person whose library contains the genres “Blues” and “Delta Blues” will see the latter will be set as a sub-genre of the former by default, and this is fully editable in a few clicks:
I understand that for you there are only 20 genres in a flat list, but we need to think about all the possible cases, and make sure everyone gets a reasonable out-of-box experience, including people with hundreds of file tag genres, people with messy genre tags, and so on.
The changes in 1.3 allowed for setting of “library defaults”, meaning you can set up your library so that everything you import uses certain information from your tags. This includes genres, but there is no way to edit multiple genres at once right now (such as being able to say "set all genres to top level"). Feel free to open a feature request on that one Peter, so we can gauge interest.
Also in the interest of clarity, note that while I understand how you’re using the word “mapping”, in the product the genre hierarchy is a different concept entirely from mapping.