Amy Lee is outstanding because she fronts an otherwise male rock group (Evanescence).
I don't understand properly the whole phrase and what does "an otherwise male rock group" especially the word "an otherwise" here precisely mean?
Learn English – Meaning of “…an otherwise + object”
meaning-in-context
Best Answer
In older English, the word wise meant manner of doing something. If you wanted to say that something happened a certain way, you might say, It happened on this wise. In the old King James Bible (1611 A.D.), we find this in St. Matthew's Gospel: Now the birth of Jesus Christ was on this wise..., whereas today we would say something like, This is how the birth of Jesus Christ took place.
While that's archaic, wise combined with other words to create words we still use, such as likewise, meaning in a similar fashion, or otherwise, which means in a different fashion. Otherwise is tricky because it can be an an adverb as well as an adjective describing a potentially different situation:
Adverb: Move quickly, otherwise we shall miss the train.
Adjective: If things were otherwise, we would have known by now.