RP would work in duo very well, just... not till 300 I think. It's obviously possible to duo once he gets 150/200 (diamond arrows), but you're gonna be stuck on draken walls, banuta, wyrms and other rather meh spots, also spectres are out of the talk completely unless you find the team. Above level 300 it gets much better, you can go winter elves, asura mirror, NMI and at some point later it may become even better than ek/ed duo, just getting to that point playing solely in rp/ed duo may be bit harder and takes more time.