Not that I am some huge Mutt Lange aficionado, but for all the knocks on him, you can't knock his results. I get it, this is a prog-metal forum, so record sales are bad, it has to sound like Slayer could have done it for it to be cool, and any song under 5.30 is shit by definition, but that Hysteria album didn't sell 10 million copies because it blows. And their current setlist isn't 50% from that album because no one wants to hear it.
I took my 14-year-old to see Kiss and Def Leppard, and after DL played, she was like "I can't believe five guys alone can make all that sound!". She was blown away.
As for Mutt: In addition to the Leppard albums (four of them): Highway To Hell. Back In Black, FTATR, Heartbeat City, Foreigner 4, Hands All Over (Maroon 5), Drones...
I'm not positive, but that gives him FOUR Diamond records (10 million sold).