With my workflow in tagging I have a problem too with that multiple-choice list of genres.
It may often be very handy not to have to write genres manually and to select the correct genre out of a predefined list.
But most of the time I miss the possiblity to set a unique genre to all marked files in the tag-panel out of a list of already existent genres in the selected files. It is not only that I have to select the genre of a very long list in these cases or enter it manually. The disadvantage is too that I cannot see in the tag-panel which different genres the selected files have and I have to define a genre-column and to look through the list.
For most of the artists and albums you have the possibility to use different genres and all of them would be right. I.e., if something is "Rock", "Southern Rock", "Country", "Country-Rock" or "Folk-Rock" can vary from the eye of the user and the position of the moon, when the user makes his choice. You only have to look at the different genres the web-sources have for the same song or album. Not to mention such obscure genres like "Vocal" or "Oldies". I obmit that I often don't remember which choice I made last time but my gain is to unify genres.
I would like not only to see a list of the possible genres to select but a list of the already existing genres in the marked files (as it its possible with all other tag-fields) and so very easy select the correct one for me out of this existing-list instead of looking in the column-view which genres exist and then take my choice.