I'd say she did work with Quincy since she and LaToya sing on PYT. The Jacksons as a group have never worked with Quincy, nor has Rebbie or Jermaine. Janet wanted her own sound, that's why she went with Jimmy & Terry as she was a fan of The Time. She did some stuff with Jesse Johnson (who was also in The Time) on her 2nd album. In general, Quincy was kind of an "older" sound and worked mostly with acts with a 'mature' audience like James Ingram. He was not someone who was popular to the youth audience Janet was a part of at the time. Also Jimmy & Terry (+ Monte Moir) were most likely cheaper than Quincy at the time as they were just getting established and was mostly known for working with R&B acts like the SOS Band. They blew up with Control the same as Janet did.