I have been to two rock concert in the past year : Brit Floyd in Bridgeport CT and Eric Clapton at Madison Square Garden, NYC (last Monday)
For Brit Floyd I was about 40 feet form the stage and treble end was an ear-splitting distorted sound - the soprano solo on Dark Side of the Moon sounded like a chain saw running at 5x speed.
For Eric Clapton I was sitting at floor level about 20 rows behind the mixing desk - i.e., the opposite end from the stage. In this case the high top end was not so distorted, but the voices were still very harsh - seemingly a massive response peak at ~1500hz. Imagine AM radio with the treble turned up 20db.
I knew a lot of the words form the songs ahead of time of course, and just about recognized them, but otherwise the lyrics were unintelligible. The only exceptions were when he sang a quieter song - e.g., “Tears in Heaven” . Clapton moved back from the mic rather than place his mouth right next to it. Then the sound was quite listenable .
Of course managing the acoustics in such a big venue is no doubt a challenge — but does it have to be this bad?