I'm not an expert on modern guitar tone, but I've lived through all the trends and changes. Like all things in music, I think it was a long evolution.
Late 70s - people were goosing Marshalls with pedals to get more sustain and distortion
1978 - EVH first used an under-powered Marshall, which introduced way more saturation/distortion than anyone had heard before.
1980s - Dokken, RATT, et al took EVH's saturated tone and expanded the music made with it, called 'metal' but was still somewhat pop songs, only the guitars sounded heavy, even the drums were thin and not heavy
1987 - Soldano SLO-100 straddled between old Marshall and more heavily saturated tone, able to do all kinds of music
1990s - 'headbangers', I started hearing way more heavy chuggy/djenty/mechanical/industrial sounding guitar music with heavy industrial beats
1992 - Mesa Dual Rectifier totally saturated tone machine; however it's worth noting when I played an early one, it was the only amp that sounded EXACTLY like a 1968 Marshall Plexi flat out, so is it really modern tone?
1996 - Krank amps founded; this was about where I thought, ok, everything's changed, they are now making amps just for a particular kind of music
...but I'm not an expert on it, that's just my impression from my experience.