Their more mainstream, pop-like metal accessibility has to be ascribed to Mutt Lange and his omnipresent, control-freak work philosophy of producing albums. Ironically, the first producer of the follow-up to Pyromania, was actually Bat out of Hell's producer Jim Steinman, and he had more of a instinctive, "if it sounds raw, nasty, and loud" its a good rock record approach to producing albums, not Mutt Lange's cerebral, technical wizardry in the studio and perfectionism attitude.
I don't know if Leppard achieves the success they do in the 1980's and early 90's if Lange doesn't straighten up the ship, sharpens them musically, recommends they fire a misbehaving, perpetually drunk guitarist and hire a more reliable, gifted one. I think the final straw according to Joe Elliot that led to Pete's dismissal, was when he showed up late one night so drunk he couldn't even record the guitar intro to song Stage Fright and the next day, Lange laughed and ridiculed it because it was so bad that Elliot was terrified Lange would quit the project, so Elliot and the band fired him.