I'm sorry to hear you had a bad experience at Evergreen, as it's probably my favourite non-vegan restaurant in Taipei. It's true that at least a third isn't vegan, however what makes Evergreen better than other big buffets (such as Jen Dow) is that vegan food is at least labelled (in Chinese) and staff are happy to assist, so you at least know the two thirds that is vegan. There are usually a few vegan cakes for dessert. I see eating at one of these big buffets as a must for anyone visiting Taipei, but I completely agree that there are much better vegan options, such as the Loving Huts, with the Guang Fu store being one of the best.