For example, it might just be possible that you don’t need much backstabbing for expert human-level diplomacy?
This article interviewing expert Diplomacy players suggests the same (though it somewhat justifies it with player reputations lingering between games, which wasn’t the case here):
Goff says his more relational strategy developed as he matured. He realized, he says, that lying in Diplomacy is usually counterproductive, especially when used for immediate or short-term gains. Double-crossing someone might help you build another fleet or shore up a front, but the moment you’re exposed as a traitor, you will struggle to build beneficial, trustworthy, and information-rich alliances with other players.
Perhaps this is dubious coming from Goff, someone who might be perceived as a master manipulator, but Siobhan Nolen, president of the North American Diplomacy Federation, aligns with the champion’s reasoning. She says despite Diplomacy’s notoriety, most of the world’s elite players eschew lies during games. Reputations linger at global tournaments. “If you’re not trustworthy, then nobody’s going to want to work with you,” she says. “You can be the best player in this game, with all the right tactics, but if no one wants to work with you, you can’t win. Top level players pick their moments to be ruthless.”
This article interviewing expert Diplomacy players suggests the same (though it somewhat justifies it with player reputations lingering between games, which wasn’t the case here):