Acorn4 just beat me to it: I'm sure that is an issue. - deafness in sound engineers as well as musicians themselves.
I sat through one concert given by a group of big voice male a cappella singers: they could have filled that hall with sound without any PA at all. But tehy had a mike each and I had my fingers in my ears throughout!
As for not being able to make out all the words: not always the sound man's fault. If the singer mumbles his way through, under the mistaken impression that it sounds so sexy (not!), the poor sound man can't help him!