FYI, you don't HAVE to work with a horrible team to get arena coin. It would be preferable to meet the specific conditions, but you can reduce the difficulty and finish the mission with ANY victory instead. The reward will be halved but at least you'd be able to get through it.

For newer player with more limited ninja pool, some of the missions really are extremely difficult and give very little option on what ninja to use. (There are, for example, very few ninja that cause blind or tag. Also if you don't have alternative versions, "use sakura" mission can get difficult etc).

So consider taking a reduced income over no income at all.