This is why I don't like most dnd dms. Ruling out betrayal because it's 'a coop game' is just as crazy as forcing every session into being a 3 hour combat encounter. If I wanted to play a coop loot dungeon crawler there's about a million video games that automate the dice rolls and loot sharing, lettimg me focus on the action and the loot.

Tabletop's role is to promote emergent story telling, not a more cumbersome way to handle combat and loot. If all a DM can do is stick to their contrived storyline and throw combat at you without facilitating emergent story telling, they're just a worse version of a video game. I'll go play Baldurs Gate instead.