Been using Simbrief from the beginning and it injects the FP correctly. If one is concerned about the realism of the FP, Simbrief shows if the generated plan is based on a IRL FP eg by Eurocontrol. And yes there might be discos eg some of the transitions into EDDM are intended for ATC to give vectors for separation. However there are also many FPs (from Simbrief) wo discos. At this point I must assume user error. If you like help post a screenshot of the MCDU of you Simbrief injected FP.