The quote comes from a new book by the Oxford historian Dominic Sandbrook, The Great British Dream Factory, reviewed in the current issue of the TLS.
Glossing swiftly over the misuse of the present tense (what they are told), the statement itself is demonstrably false. Bach, Handel, Mozart, Beethoven, took orders from no-one. Nor, so far as we know, did their predecessors.
Being a good musician was always a transferrable skill. If a player didn’t like the orders that came down from on high, he did a midnight flit and set up in the next town, province or kingdom. Musicians were ever a discomfort to their patrons. A few, like Haydn, might have bowed the head in the interest of a quiet life. But Bach often bucked the system and Handel set up his own business in London.
On the basis of what we know of the lives of leading musicians they may have pretended sometimes to do as they were told but seldom did. Sandbrook needs to clarify that horrible generalisation.