In my opinion RW TP are not so different from FW TP ! Of course the aircraft are different from each other because of the way they fly, but the job of the TP is not.
And also France is starting to mix their TPs. I now even know a French TP working at Istres (home of EPNER) who was trained at ETPS (hello Eric).
For me, the reason why there are less RW SETP members could be that there are simply more FW aircraft than RW...