jim rozen writes:

You're the perpetual motion advocate. You assert that an expanded
quantity of air represents the same energy as the compressed equal
quantity out of a reservoir,

Incorrect.

OK, so you don't assert that. You must believe (with me) that "same
energy" above should read "different energy". So you must agree with
this:

(1) An expanded mass of air can provide less attainable work than the
same mass when more compressed.

And thus the following:

(2) A given mass flow at a higher pressure holds less attainable work
flow than the same mass flowing at a lower pressure.

(3) A regulator, since the input and output correspond to the
alternatives of (2), must necessarily introduce a loss of attainable
work in the output versus the input.

(4) Which is to say, regulators are inherently inefficient. They
dissipate some of the available work into (ultimately) waste heat or
work performed on the atmosphere.