You have left out some very important parts of the equation.
1) The room itself has a huge impact on the sound. There are places that you will never hear a good concert - the room is simply that bad.
2) If the room is good, then you wold tend to blame it on the "sound guy" - leaving aside that some of the best FOH people aren't guys, we'll take on one other detail - for a bog tour, there are 2 "sound people" - there is a "Systems Engineer" who is responsible for getting the PA set up and tuned to the room so that you can make a good mix - if you ask the FOH person to do that, some don't have the skills (Systems Engineer is a highly technical job), and even if they do, the process is so hard on your auditory attention span that its essentially impossible to mix well after that. The FOH person comes in after the system is set up and tuned (with fresh ears) to mix. If either Engineer doesn't do their job well, the sound can be a mess, and who is at fault? You (the audience member) won't know.
3) The musician is responsible for doing their job well, but if they are a "hired gun" (not the name on the marquee) then what they play and how they get their sound are things that are team efforts - there will be someone who is a music director who hires and manages the musicians and the FOH person and the musician will work together to get good sounds that can work in the house mix.
Sound for a concert is not a single person's responsibility - it's a team effort. Given that, if the team dynamics aren't good, the sound may suck simply because the people aren't working well with each other.