This is incorrect, many coop games give un-loosable ELO which acts as a great way to see opponent experience. Some other games like Hanabi had ELO that you could lose but it never calculated players as having tied each other, you won as a team or lost as a team.
There are over 100 pages of complaints against the ELO changes that BGA made, including hiding ELO from coop games even though it is still earned or lost accordingly. They have never responded to any of the valid points and show their true colors as not caring about their player base since the site was sold.