Honestly, Rose has followed a pretty similar trajectory as Bronco. Both inherited losing/mediocre cultures. Both revived the programs and had signature seasons about 5-6 years into their tenure (2009 finishing #12 and Jimmer's sweet-16 run). Both had 5 or so years of ho-hum seasons (Bronco with a string of 8-win seasons, Rose with a string of 10-12 loss seasons).
I don't think BYU needs to fire Rose. (I don't think BYU was ever going to fire Bronco either) But I don't think it's terrible to question the trajectory of the program. It certainly doesn't feel like BYU basketball is trending up, which is not good considering BYU just had their worst season in the last 12 or so years.