In the CL you will only find clubs at your managerlvl, opponents can vary as much as in your league, they can be 2-5 star teams. Obviously, as it's a format for the best 4 teams of the previous seasons league. A Cup's roster is purelu based on avg quality. As a result, with a high Q team, you´ll have a dificult Cup lvl, as a low Q team you´ll have an easier one, but will stand less chances of winning the CL.