What is reversibility? I mean really, what is it?

Nonsense Reversibility Cannot Affect Efficiency

Energy or Probability Reversibility of the Work Curve requires no extra energy

Rule of Crayons All engine cycles are reversible by Kelvin & Carnot\s use of the word.

Reversible Diffusion Reversible Diffusion

Almost reversible... Almost reversible Heat Transfer, counterflow heat exchanger device efficiency limit approaches 100%

Reversible irrelevant Why? Because the law of conservation of momentum (and energy).

Foreword: This section explains what Reversibility is, and why it does not matter.
REVERSIBILITY HAS NOTHING TO DO WITH EFFICIENCY.
Repeat, nothing.