Jaywalk3r, the article I linked you, written by Bernhard Rolhoff, found a derailleur-equipped bike to be up to 99% efficient. Did you read it?

A bicycle is not 99% efficient. The drivetrain is 99% efficient at transferring energy to the wheels. Any losses from tire pressure, wind, or load are neither here nor there.

If my derailleur is failing, I can easily see it coming long in advance. I can gerry-rig a solution using found parts, fiberglass paste, coca cola cans, JB weld, hot glue, crazy glue, zip ties, paracord, etc. I can even remove it in two seconds and run SS back to civilization. Bent derailleur cages can be re-bent, derailleur springs are easily replaced, missing derailleur screws are found all over or suitable replacements can be bought at hardware stores, and pulley wheels are interchangeable across hundreds of models, globally sold.

A Rolhoff is not field-reparable. It's completely enclosed, has an embarrassment of minutia ad infinitum, and needs to be kept completely clean while being worked on.