Audio output levels between applications

while there may be a more technical solution the simplest one I've found is this:

set the master volume on your computer to a higher level

turn down your master volume on your monitors to a lower level (if your power source is ample you will get a steady signal at a lower volume)

adjust the volume of your audio streaming as high as you can before it clips.

any application running audio that has an overall higher output than another application will be throttled by the master of the computer.

the inherent problem can be summed up in your sentence "the range is pretty huge"

what comes to mind were those TV's that would adjust the volume of commercials that were engineered to be louder than the show you were watching/falling asleep to. There might be some 3rd party software to do this but the cranking or dropping the master on the computer and brining everything up to a max, it's in many ways like recording a song where you have different instruments and set unique levels for each one as you add the track.

I'm sure that this was never an issue before - must have been a change within Mac OS along the way.

Wrong, it's has always been an issue. There is no standard output level for apps, it has always been an approximation.