Perhaps it depends on who is counted as a fan?
The Black Album sold millions more than Ride the Lightning or Master of Puppets, but the 'true' fans are arguably those who got into Metallica with the earlier albums.
With Anthrax it's a bit different since their attempt(s) to become mainstream with Bush basically failed through a combination of the music scene changing, record company indifference, and their own bad career decisions. Maybe the 'true' fans are those who don't have an axe to grind on either the Joey or John eras?