A typical Kubert Rock cover from the 1970s. In those days of newstand distribution, the theory was that the cover is what sold the comic book, not necessarily what was inside.
The intention was to leave an excited question mark in the mind of the potential reader who would then buy the comic to discover the story within. Unfortunetely, for some of those comic book publishers, the interior story didn't have to deliver on the promise of quality/interest, just the cover getting across its function of selling the book was enough.
As Jack Kirby was known to say in reaction to this marketing strategy (he was with DC in the early 1970s) 'they'll buy a few issues this way but they won't come back."(Paraphrase)
By the end of the 1970s, newstand distribution was mostly dead.
To me, Kubert's brush work has always had an impressionistic painterly feel to it
Rima cover art by Kubert, issue #7, 1975 DC Comics
Review: Joe Kubert Tarzan #214, November 1972
Joe Kubert Tor #1 "The Outcast" DC Comics July 2008
Joe Kubert art from Tarzan #214 -1972 DC Comics - Page A
Joe Kubert art from Tarzan #214 -1972 DC Comics - Page B
Joe Kubert Sgt. Rock Cover, November 1976