During what time period was Prince recognised on a media level as a genius of modern music? Was there a known article/journalist who first used it?

Hmmm.Possibly the Dirty Mind era. Prince had to sing about have intercourse with his sister before the media really got hip to him or at least paid him some mind

.When You Were Mine(namely) was recognized as an early classic that showed Prince as being more than your typical R&B act.The DM and Controversy tours established his live shows as something not to be missed.

By the time the 1999 album and the Little Red Corvette single came about,mainstream realised he was something more than "the imp of the perverse".When Purple Rain came out,all the critics had climbed aboard the purple bandwagon.

Oh yeah, it was most likely Minniapolis reporter Jon Bream who made first mention of P's brilliance on paper.

Kurt Loder gave genius props to Prince in Rolling Stone in the early 80's.

Jon Bream or Nelson George