2 different solutions to this issue. First make all new versions of old raid primaries into exotics while retaining their element. This forces you to either use a normal weapon and have an exotic heavy or secondary or use normal heavies and secondaries with an exotic raid weapon. Second option strip the elements off the guns and leave them as legendaries. Fatebringer was awesome due to a number of reasons not just for its arc damage so it would still be a nice gun.