I think the loop is mains to singer's mic, because the stage is cramped, so robbing Patsy to pay Pete is a wash.
They want to lower the overall volume so they can turn down the PA and keep the mic gain. The only way that works is with drummer playing ball.
Drummer must be either deaf or hasn't got the vocal in his IEM mix. Having him blazing away to his own IEM mix is the beginning of the problems.