I think some are getting off base as to the intent of the question.It is an archery question.
For me compound is more challenging BECAUSE my goals are much higher.If I can hit a pie plate at 20-30 yards with a traditional bow I am happy(I can usually get that in a short period of time) but if I can't hit a 1" dot at 40 consistantly,I still have work to do in my mind.I have days when I can do this but more days when I can not.And I work at it ALOT.
Yes,the traditional equipment is harder to master but the the question is it more challenging.It is really in the mind of the bowholder.
For someone else the traditional may be more challenging because they don't have a goal of hitting 1" dot at 40 with either and are just worried about what kind of group they get at 20 yards.