Really, you figure the sonatine is more difficult? I don't play the scherzo, but it seems like it would be much more difficult. I think the length of it is around that of the sonatine, 'page wise not timewise. It sounds like there are more drastic leaps, and the fast sections sound a bit more difficult than those of the third movement of sonatine. If the sonatine is more difficult, then it would only be because of the third movement IMO.