There has been a de-facto HF standard for 60 years.

The USA military first used it in specifications of radio equipment when
placing contracts with manufacturers around the end of WW2. There may have
been some restrictions on publicity at the time.

The Standard is 6 dB per S-unit and 50 micro-volts into 50 ohms at S=9.

Therefore an S-meter is essentially a power or wattmeter.

The Standard is quite logically derived.

The 6 dB fits in very nicely between a typical receiver's internal noise
level (S=0) and a typical receiver's signal overload point (S=9+30 or 40
dB).

S=9 is about half way up the scale which is linear in dB's, or S-units, from
one end to the other.

There's nothing wrong with the standard. If your S-meter reads incorrectly
then don't blame the standard - re-calibrate the meter. If you can't
re-calibrate it blame the poor quality of the meter.

I have two relatively modern commercial transceivers plus two home-brewed
transceivers. Their S-meters are accurate enough for the intended purpose.
What more should I expect?
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Reg, G4FGQ