It all depended on the recordings. Tying all classic rock into one lump won't do it justice. Prime example Tommy Bolin's Private eyes and Teaser, both vinyl from the mid seventies, if you can find better bass anywhere, in any genre, or any period, I would like to know about it.
However the majority of BIG classic rock bands used very average recording methods back then since their name alone was enough to sell records. I find the lesser known bands went much further out of their way to hire better technicians to get a better quality sound in hope of being discovered. And it is a good thing for me since most of my collection is off the mainstream bands.