The default volume level of 74% on Pulseaudio slider cubic scale used by Wireplumber feels a bit high, especially on Bluetooth devices where this value is uncomfortably loud on all devices I have.
It's also applied to input direction, where 100% might be a better default. So it's maybe useful to reconsider these defaults -- here's another suggestion.
It's safer to have the default volume value at significant attenuation, to mitigate situations where the output is at high gain.
Use linear scale 0.4^3 (-24 dB), which puts Pulseaudio volume sliders at 40%, as a better starting value than 0.4 (-8 dB / 74%). E.g. for many Bluetooth headphones, the volume at 74% is still uncomfortably high, and a lower value is better.
policy-default-routes: use different default volume for input direction
Input direction volume doesn't need a safety margin.