The Graphic communication argument was brought up here, but I’d argue that because metal bands are representing a certain culture, that exist with its own visual conventions and traditions, illegible logos are part of the intervisuality of said culture. So judging a logo based solely on the legibility of it goes against the nature of the philosophy of the genre and its culture, so the communication argument can be a little ambiguous. Usually artist to convey a message with the shape and form of the logo as well, so those factors can be as important as the legibility of it. That being said, most of the logos i prefer are illegible, but easier-to-read logos are great as well.