This is a very good starting point, and it's really what you can generally control as pro sound provider. But if the acoustics are bad enough, it generally trumps many of the benefits of a great sound system. The proper remedy is acoustic design and treatment.
A caveat about acoustic design and treatment. The ideal acoustics vary depending upon the type of ensemble. A small acoustic chamber group can sound fabulous in an extremely live room. A larger acoustic ensemble is likely to sound better in a less reverberant space. Amplified music tends to work better in spaces where especially the low frequencies are well damped. Here's an article if you are interested: ICA2016-0095.pdf
Maybe, maybe not. But if you are regularly being asked not to use a preamp you are at least playing the same stages as him.
How is that relevant? I've never had a single foh engineer reject or complain about a preamp signal I've sent them.