Heavier than an RB with a WLF...maybe, heavier than an RB with a prism, probably not. The lenses are lighter weight too because they don't have shutters in them.
Also, film advance/shutter cocking is not a two step operation on the Pentax or Hasselblad as it is with the RB, and mirror-lockup is less of a pain in the rear on both of those cameras as well.
As to fashion people loving RBs, that I'm not so sure of, but I do know that an RZ or three was in the stable of pretty much every fashion photographer by the early 90s. Magazines no longer wanted chromes for the majority of assignments, and were heavily biased towards medium format as far as cover work was concerned. Editorial work was more free-form, and my dad used to enjoy the chance to shoot films like 1600 speed fujichrome in his Nikons for parts of those assignments.