Also, whether you like it or not if you make a game co-op it has to be built around that to make it work from the very beginning which does change the basic gameplay. You can’t have two spider-man zipping around an area, without sacrificing the balancing for single player, or the performance. There’s always a give and take when you include multiplayer in what was originally a single player game.
An additional mode like Tsushima legends would make sense and i wouldn’t be surprised to see it, i think Insomniac is working on a multiplayer thing