In response to

so your argument is that everything else around is lame, so how could hip hop escape the general lameness?

there's an element of truth to that but the fall from that Missy/Timba/Neptunes/Jay-Z/dirty south peak is much steeper and dramatic than e.g. indie's steady-state through the decade, or dance's endless plateau (i actually think indie has got a lot more interesting/adventurous -- and actually higher in profile with vampire at #1 billboard -- in the last few years -- but totally agree that dance music is no more innovative or mainstream-dominating than hip hop -- in fact i made similar 'death of dance' arguments back in the early noughties, to similar upset from people who were scene-boosters -- and dance's decline from its nineties peak was undeniable, the whole superclub/supsterstar dj thing had plummetted circa 2002-3, the top 10 hits for dance trax weren't happening . the analogy with what happened to hip hop later in the decade is very close -- booms do lead to busts, generally speaking!)

re the 1989 argument, judging by sales will never give any real benchmark of cultural impact -- i don't know how old you are or whether you were conscious then, but De la Soul and especially Public Enemy had a cultural profile way way in excess of their sales (which weree't minor, PE had UK top 30 hits with rebel wtihout a pause, welcome to the terrordome, bring the noise etc)

there's nothing in the current hip hop demi-underground that has anything like the talked-about-ness of De La Soul, PE, jungle bros, etc -- magazines were all over that shit, at Melody Maker we had these people on the front cover -- and MM was an indie/Goth paper in large part

actually i wasn't even that keen on the Native Tongues type stuff, for me the 86-88 stuff was the killer phase, rap's first golden age , def jam, eric b rakim, mantronix, LL/beastie, early salt n' pepa, tons more.... all that stuff was sonically cutting edge AND commercially successful, it wasn't underground at all either by ambition/mindset or in chart reality, and it was the most cutting edge stuff give or take a Marley Marl (who i'm sure sold way more than Gonjasurf or whoever nowadays)

90s was a pretty steady upward graph line w/ -G-funk,, cypress hill/house of pain, wu tang etc and then boom, another commercial-yet-avant-garde, street-yet-futurist golden age late 90s/early 90s with the above mentioned

what's striking now is how conservative the underground in rap is, same old glitchy prefuse 73-ish stuff, or digging in the crates type antiquarianism, i mean it's niiice, some of it, Dilla obviously

as i say i don't know how old you are but it struck me as a symptomatic piece of writing in so far as to big up the present required downgrading the past, denying there were ever these peaks and surges.... and then equally the argument for hip hop being still vital turns out to be that nothing much else is that vital so why should poor old hip hop get picked on...

you're right though that there's no timekeeper for pop -- black music of one kind or another (usually US, sometimes jamaica) always had been the energy pushing pop -- it was what was generative of new forms and expressive modes ... but that's gone now, seemingly.... the question is if anything will replace it, or can replace it?