OP, I don't think they are frumpy. They are a certain 'look', but I wouldn't say frumpy.
(But personally I do think appearance is more important than comfort. So if I couldn't find a comfortable sandal, for eg, I'd get another kind of shoe instead, not a frumpy sandal, if you know what I'm trying to say!
I've had this argument with friends many times and all I know is, I would be much more metaphorically uncomfortable wearing something I knew was frumpy than I would having a physically uncomfortable item of clothing. Crazy, but that's how I feel!)