Very high level players with very powerful counters can probably still take them solo but they're much easier with a friend. (imore.com)
At high levels players can even jump into each other's game worlds to team up and fight monsters, or murder each other. (pcgamer.com)
We have so few high level player coming out of the academy, we may sell a couple for a few mil but we spend an amazing amount to get those few. (justarsenal.com)