The issue here is that quality and enjoyment are 2 different things. The former is absolute and the latter relative. Quality is a parameter, that in this case belongs to the orchestra. It can be defined by using measuring units of intonation, synchronization, dynamics, ensemble sound and artistic impression. This is a standard method for artistic competitions worldwide. There are piano, violin, trumpet, ensemble competitions, where we even have a fixed set of rules to „judge“ everything from school level to world class performances.
Now, every instrument player starts building their audience from their first notes. At first it is the mother or an aunt. As they progress, their teachers and friends join in, later, they get critical acclaim from external institutions like newspapers, critics.
Actually, the quality only is what it is. Only enjoyment can be poisoned if we are not the intended target audience. I experience this when I adjudicate competitions (mostly at school or college level). Some judges judge absolutely - which means that the intent of the competition (promote children playing musical instruments) is not upheld. I find that often this type of judge is a frustrated player that never got their own chance. By criticizing others, they raise their self esteem. Others try to be friends of the performers being overly positive about everything and conveying a false view of what the performer did. Yet others give a score but no justification.
So, getting back to your semi professional event. Is the problem a group of 80 musicians trying as hard as they can, having fun while doing so or is the problem that we went to the concert in hope of better? I play with professional and semi professional ensembles. My measure is: on the trip home if I ask why I even said yes to the gig, then I do not do so again in the future. It is MY JOB to test the waters before jumping in. After a while, the performer either has a lot of quality gigs - or none...
Whenever I feel blue, I start breathing again.