Plenty of working musicians (and part timers I should imagine) who read AND busk, take solos on heads and are excellent at many styles.
So the bit about cruise musicians (above) is rather silly.
Classical musicians, are a different entity all together. They are often playing many different things within one piece.
They might be playing the tune/theme, they might not. They might be playing part of a tune for several bars before another section take the tune.
They could be playing divisi chords, harmony lines, counterpoint lines, different bpm's, several metre changes, the conductor pulling the tempo all over the place,
or even 40 bars tacet, trying hard not to get lost. Then you get the soloist that remembers complex solos pieces.
The Repertoire changing every season, short rehearsal times for complex pieces. It's all very much worthy of music stands.
So to turn up and just 'play' is quite often alien to them. The OP band needs to have a compromise really.