By that criteria, Baumol's doesn't even apply to symphony orchestras. Technology has made symphony orchestras marginally more productive. Instruments are better and more consistent, recording technology improves practices, et cetera.
Baumol's applies to anything where technology has improved the field significantly less than average. That includes both symphony orchestras and janitorial services.
If the function of a symphony orchestra is to perform symphonies, there has been essentially zero change in their productivity for several hundred years. Contemporary instruments are no better than they were in the mid-1800s. Their rehearsals are rarely recorded, and even if they were, it is much less common for this to contribute to future rehearsals.
Wikipedia says that Baumol's is:
> the tendency for wages in jobs that have experienced little or no increase in labor productivity to rise in response to rising wages in other jobs that did experience high productivity growth.
while it's not the canonical source for the definition, it is notably more specific than your version.
Baumol's applies to anything where technology has improved the field significantly less than average. That includes both symphony orchestras and janitorial services.