You are over thinking it.One thing nobody has really acknowledged is the lack of a rehearsal/stage sound check prior to performance? Shouldn't most places do this? The venue I'm playing it is not. We have to show up after a band and get on as quick as we can and play. I'm worried the sound guy (if there even is one) wouldn't know our levels. Is this an irrational fear? Maybe I'm just overthinking it
A sound guy will set levels as he see fit unless he is employed by you. A good sound guy will have you dialled in very quickly, especially if you are not first on the bill.
I somehow doubt that a venue will provide a PA for a multi band event and not have a sound guy.
I have only played one venue that provided a PA that did not have a sound guy, it was so abused it was virtually unusable (scratching subs, blown tweeters). We only used it once and it was so bad, we took our own for future gigs.