> Serfs were not only expected to provide labour to their “employers”, but to fight for them

That was never expected. It was never going to be expected. Fighting was much too prestigious for serfs to be doing it.

> believe what they believe

This changed over time. Mostly serfs were too unimportant for their non-Christian beliefs to matter. But it was always a formal expectation, and as the centuries went by it did develop into an actual expectation.

> and pledge their fealty.

Indeed. This is the difference between a W2 worker and a contractor; it escapes me why so much public rhetoric focuses on W2 status as if getting it were a victory for the employee.