Categories should be based on speed. With your ftp, height and weight zwift could work out your projected / baseline speed for the course and place you in a category. I guess this is what Autocat does.
It would be great to see your projected speed for each course and how you compare to other riders, then you could see which courses you were best suited to. You could be A cat for Alpe du Zwift and B for Fuego flats.