Moon Knight took on a Werewolf and survived. You mention that both will have ten minutes to prepare, I'm sure Moon Knight would deal more deadly weapons than just boomerangs and brass knuckles if he knew he was getting in a gun fight. If he's just used to fighting stronger foes with just those weak weapons, imagine if he used ones that fit his mercenary lifestyle, if it's a fight to the death.
Moon Knight happends to have adamantium weapons as well, and when that metal's involved, probability goes down significantly. Also, I think Taskmaster is a more formitable villain than Crossbones and he still lost to M.K..
Moon Knights is just a better character, and the better character takes the popularity of a writer's mind.