Quote - i'm sorry i'm being a pest, but could you explain how all the print programs, designers and printed scales i know of are wrong?

Because it doesn't make a difference for them. While non-linear (127, 127, 127) is not physically 50% intensity, it just happens to look exactly 50% gray to the human eye on a calibrated monitor or printer. If all components in the chain agree on what (127, 127, 127) stands for, everything is fine (sometimes two wrongs do make a right).

However, physical calculations like fresnel equations or Lambert's cosine law work only correctly when they get physically correct input. That's why for rendering we need to convert between perceptual values and physical values.