Damn you folks, sent me onto a deep dive where I found this, which is a partial and imperfect answer.
https://en.wikipedia.org/wiki/Weber–Fechner_law
As a biologist I would say one reason why the ear can cope with both a huge range of sound levels and doesn't respond linearly to volume is that it has tiny muscles that 'tighten up' the system to mitigate damage by 'turning down the volume'. I looked into this in a bit more detail:
https://en.wikipedia.org/wiki/Acoustic_reflex
The reflex clicks in for sounds over the threshold (which can vary between 70 and 100dB). A sound 20dB above the threshold might be reduced by 15dB. A reduction of up to 20dB is possible.
It takes 2-3 seconds to click in (which is why being close to drum hits is just so horrible). There are lots of subtleties.
Also, it click in automatically to give ~20dB reduction just before you speak, so if you are expecting sudden bangs, try talking to yourself...