How much of our favorite pop music would never have existed had the artists not been stoned completely out of their minds?

You might be correct, as much of the 'pop' music had its roots in older rock, where all of them were stoned, except for Ted Nugent.
Do you think the writers of Spongebob and South park were stoned. By the way what is a good definition for 'pop' music?

From the 60's and 70's, over half.

From the 80's.... ????  they were well beyond stoned. (what the heck is a Flock of Seagulls?)

After that, they were all addicted to stoopid.

Billie Holiday notwithstanding, the "sex and drugs and rock and roll" scene really got its kick-off in the sixties.  The Fabs each had their preferred mood alterer. All four were introduced to weed by Bob Dylan, it remained Paul's go-to (in the "English garden" sequence in I Am The Walrus you can SMELL it). John was dropping acid, George doing coke and Ringo popping downers.
Syd Barrett (the "Pink" in Pink Floyd) melted his brain, it landed him in the funny farm. Hendrix's penchant for recreational pharmaceuticals may well have enhanced his creativity but it also seriously shortened his life. The Stones were doing everything they could lay their hands on (nobody knows how Keith Richards is still alive - my own theory is that he's a zombie). Jim Morrison and Janis Joplin both died from heroin overdoses (Morrison was aichmophobic, he snorted it - his girlfriend, Pam Courson, had a serious smack habit).
Beethoven and Mozart were known drinkers (I've fallen into a creative reverie myself when slightly drunk), and most of Britain's poets of the romantic period were hooked on laudanum, so it isn't new either - but the sixties were when it took off.