The MMEL will be written by a group of people that includes the same 'folks' who write the RFM.
To clarify: that may be true in your part of the world, but is not in the U.S. The MMEL is approved by the Aircraft Evaluation Group, which is a part of Flight Standards (ie, operations). The RFM is approved by Flight Test Pilots/Flight Test Engineers, as part of the certification requirements of Part 27/29; they need not be included in the MMEL approval process, although that would be ideal.
In fact, the MMEL grants relief to the RFM because an aircraft doesn't meet its type design (meaning everything is installed and functional). Consequently, RFM limitations (say, for a busted AFCS) assume the failures occur in flight; the MMEL assumes they occur before takeoff and are known to the crew. Therefore, the MMEL may impose additional limitations, such as minimum crew requirements or flight conditions (VFR), in addition to when the corrective action must take place.