I'm not one that subscribes to the idea that it was Grunge that was solely responsible for making the 80s hard rock obsolete.

In August 87 Appetite for Destruction came out & GNR was portrayed as the band that would rid the world of the pretty boy poser nonsense. To most of the people I knew at the time, this meant that the likes of Winger, Nelson, Warrant etc. that followed in the next 18 months were anachronisms, albeit ones that still sold massively in the US for a period.

The fresh new music was Jane's Addiction, Kings X, Faith No More, Fishbone, Warrior Soul etc. They all had a mixture of styles & lyrical maturity that was lacking with those bands that eventually became labelled Hair Bands. And don't forget the impact of Metallica etc.

When the press started using the term Grunge it related to Mudhoney, Tad, the Melvins etc. The name fit those bands but by purely geographical coincidence the likes of Mother Love Bone were placed in the same category & from there it seemed to be applied to the rest of the Seattle scene when none of the bigger bands sounded alike.

The grunge bands really were hard rock bands that could cross genres and be embraced by both metal fans AND alternative fans but so were the likes of the Chili Peppers, Nine Inch Nails etc.
In my opinion it would have still happened without Nirvana & Pearl Jam.