I completely understand the example of your wife’s vocal power/control. At one time I played and studied the trumpet. As with any instrument you have much control over the volume you wish to provide. If I wanted to I could blow people out of a decent size room with just that single trumpet. The thing is that horn sounded just beautiful played at moderate and lower levels.
As you mentioned, audio system resolution seems to be the key factor. As this aspect of my system improved over the years I discovered I could immensely enjoy music at lower SPL levels. I’d say a very good parameter for a system is how satisfying is it to listen to at low and moderate volume?
No question however, to each their own choices. I know that some like to listen regularly at SPL of 90db and above. Their ears and enjoyment be served. It just isn’t for me.
Charles