"I believe WOW is a work of flawed genius," Barnett said during the Develop Online conference in Brighton.
"When you dismantle [these works] you can never be sure whether you get genius or flaw. The reason I don't play other online games is that they're corrupting, they are cancerous, they change the way you think."
He gave an example of a change in quest structure in Warhammer Online, away from the standard set by World of Warcraft.
"That one change took three months of meetings, because the people I was up against were corrupted by the gaming experiences they'd had.
"They weren't capable of thinking sideways because they knew the answer, and it worked, and resulted in a game that is very successful."
And emulation of the market leader isn't a wise tactic either, according to Barnett.
"You can't be the Beatles. If you try and be the Beatles, you'll end up as the Monkees," he joked.