It's not a matter of opinion. Classic rock is a recognized genre. It's guitar centric rock and roll from the late 60's through the 80's. It's important to understand this when you stroll down the classic rock isle or tune to the classic rock station.
If you want to hear Elvis or Buddy Holly, you'll have to tune to the oldies station.
So the word "classic" to which you refer (and,perhaps,subscribe) is more of a trademark whereas my use of the word is more in line with the standard definition found in the Oxford Unabridged.