No RTR (Radio Telephony Restricted) and CPL (Commercial Pilot License) are too different and it is not quite fair on comparing their difficulty. Licensing Transmission RR is predominantly a licensing requirement to communicate in aviation, including the learning appropriate radio procedures, aviation rules on communication and using the English language. It demands learning a part of the regulations practicing the transmission and successfully passing through a simple written and oral examination. Although it is a must of safe flying and obligations it is in general simpler and faster to fulfill than a pilot license. The RTR exam can be overcome with appropriate advice and a few attempts and therefore is not as challenging as other parts of pilot training.
A CPL on the other hand is a detailed and more challenging license as it needs in depth aerodynamics study air system, navigation skills weather and law of aviation as well as a vast number of flying hours. CPL is much more difficult than RTR, requiring thorough theoretical classes followed by a practical training in the simulators and in actual airplanes. So although the checks and balances of RTR are essential and fundamental CPL would require far superior skills knowledge and time-consuming.