'different people have different perceptions, and expectations, and you'll never please everybody.'

Nice platitudes. Now how about some science?

If there is feedback, then equipment is either set up wrong or too loud. Figure it out - before the concert.

If people are feeling pain from the sound, then it's too loud. What is the decibel level? Figure it out.

If 3/4 of the audience have left, something is wrong. Figure it out.