Pedantic
Legend
Yeah, my point is that this is not on the cooperative/competitive axis at all. You're asking a question about difficulty and/or the floors and ceilings on skilled play. Setting the balance of impact between player actions over the underlying difficulty of the game, the "viable" part of your formulation, affects the end state of the game considerably.Sorry, not my intent. The point was exactly that there's an incentive to make the best possible choices whether the game is cooperative or competitive, the difference is that bad choices, in a competitive game, will lead to you losing, which is to bad for you, but fine for the player that wins - depending on the player, it might be annoying due to the lack of challenge, or not, if it's just all about winning for them. Avoiding bad choices is part of the challenge, and making better choices than the next player is part of what winning is measuring.
In a cooperative game, bad choices hurt all the players, and making a better choice than the next guy is not necessarily going to help you win, while everyone making the best choices will help you win.
I am generally of the opinion the reward for bad play should be knowledge of how to play better in future, delivered by loss, and that principle does not change if victory is evaluated as individuals or in a group, though it becomes harder to evaluate the relative impact of each decision when you spread them out amongst more people. I do know some people who play cooperative games with players of varying engagement levels essentially as an extra challenge. If you can't rely on your team to consistently make the best choices, can you still win?