99% of concert performers use Monitors to hear their own performance over the crowds and have nothing to do with the loudness of the audience speakers. Stage Monitors can be just speakers at the front edge of the stage pointed directly at the band [1] or they can be sound isolating earpieces so artists can hear exactly the sound mix they want [2].

[1] https://audioinstallations.co.uk/blog/stage-monitors-how-do-... [2] https://www.newsweek.com/taylor-swift-eras-tour-cruel-summer...