Don't agree at all. Lots of classic rock bands appeared and peaked after that. Deep Purple peaked with Made In Japan 72-73, Led Zep, Rainbow, Rush, AC/DC, ZZ Top, Sabbath and then you have the Metal bands like Iron Maiden, Metallica etc there are far too many to list.
For me Rock music peaked around 74-76 altho for some it would be the Iron Maiden era i reckon.
Dave