Hen, It is easy to criticize sound engineers and difficult to be one. Every auditorium / room / hall / outdoor gig has its own acoustic and natural echo (Or lack thererof) profile. You have to zero the room first. I use a "pink noise" generator to evaluate each room.
Then, ya gotta have a lot of patience with "Artistes".
You have to have a good knowledge of the sound frequencies of human vocals and various instruments. When someone sings you have to quickly get their best range nailed down so that it sounds as warm as you can get it.
Most of the good SEs I know are also musicians themselves and drifted into the job because the SEs they were using sucked! I've played in rock and folk bands and specialize in acoustic sound these days. I'm told I'm good by performers and audience alike.
Amplified acoustic sound is an art of using the various EQ devices/reverb units to get the sound the artist(es) is looking for.
I can make you sound as good as you can be, but if you sing off-key or your instrument is not in tune, I can't fix it. I can tell you through the monitor that it is out of tune but I must wait 'till the end of the song.
It also helps to have a CD of the performer to listen to before the gig so I know what they are supposed to (want to) sound like.