Is there some kind of generally agreed-upon “degree of difficulty” scale for musical instruments ranging from easiest to learn how to play proficiently to most difficult? For example, is it harder to become good at the clarinet than the piano?
If such a scale is too subjective to cover all classes of instruments, I would think it might be easier to do so within classes of instruments, say brass, woodwinds, and strings. Is the trombone easier than the trumpet, or is the viola easier than the cello?