I hope he was appreciative of the advice.
I’m not being facetious for once, one of my bugbears is poorly implemented sound at live venues, especially when you absolutely know it’s nothing to do with the venues acoustics.
The last reasonably sized gig I went to before the pandemic hit was to see one of my favourite songsmiths, Michael Head (He’s had various bands, The Pale Fountains, Shack, The Strands). He doesn’t tour very often, so it was a rare treat to be able to see him live. Especially as he’s a Liverpudlian, and the gig was in Liverpool.
The sound system was fine, because the support act sounded good, but when Mike came on he was utterly lost in the mix, drowned out by the lead guitar and drums which were way too far forward in the mix.
Unforgivable given that his music is driven by the lyrics and his gentle vocal performance (usually, he’s more than capable of belting it out if he wants to). Unfortunately I couldn’t get to the sound desk or I would have done the same as you.