Why does it have to have an Elo system anyways?
It's not a competitive game. Players are not playing against each other, therefore they need no ranking.
Elo system was design to measure a player's strenght and his likelihood of winning against another player who also has an Elo rating.
Players are not trying to win over each other. It's a coop game. It would only make sense if it was a team of 2 against another team of 2.
"The Elo[a] rating system is a method for calculating the relative skill levels of players in zero-sum games such as chess. It is named after its creator Arpad Elo, a Hungarian-American physics professor.
Zero-sum game is a mathematical representation in game theory and economic theory of a situation that involves two sides, where the result is an advantage for one side and an equivalent loss for the other.[1] In other words, player one's gain is equivalent to player two's loss, with the result that the net improvement in benefit of the game is zero.
The difference in the ratings between two players serves as a predictor of the outcome of a match. Two players with equal ratings who play against each other are expected to score an equal number of wins. A player whose rating is 100 points greater than their opponent's is expected to score 64%; if the difference is 200 points, then the expected score for the stronger player is 76%. "
