Perhaps the most annoying myth in audio of 2025? Talking about Loudness!

I believe all you said is based on science and for you your listening level has hit the sweet spot.big kw amps have a higher level to handle transients.they are not running 90 percent of thier spec.power is voltage times amps.it is when you push your amps into clipping you get distortion.alot of my amps have the same distortion from 1 watt to 1.2kw look at the mcintosh 1.25 kw amp spec.they have protection that helps them avoid clipping.some of these amps have 50 transistors per monoblock.they run at a low percentage of thier maximum so low distortion at high levels.class d is very clean.now if I run my chifi amp rated 100 watts that has very little transient it will distortion. Speaker manufactures list thier spl or efficiency for a reason.some like infinity kappa 9 are known to be amp killers.my magico q7 look at jays audio review ,they need power to perform due to thier design.while my klipsch are very efficient.look at the hegel h30a monoblock numbers in the reviews.d sonic has a 2kw amp low distortion under 2500$. What a bargain and great to live in this audio age.you may be having an experience where your stapedial muscle in your middle ear tenses up to prevent your tympanic membrane from moving so much it's called recruitment of the vestibular cochlear nerve,the hearing nerve to logarithmic increase fire rate and can be painful in some people I'm glad you found your sweet spot for you and your equipment.its a great hobby based on science with some snake oil mixed in .like all things in life we just need to find the truth for ourself.enjoy the music nomatter what the level is.

I tend to agree with @carlsbad2. If your system does not sound good at a reasonably low volume level, it needs work. Fortunately, the work doesn’t need to be substantial, and you don’t need high-sensitivity speakers to achieve that.

In my rooms, with an ambient sound level of 25 dBA, 65 dBA is pretty loud to me. I usually listen at 55 dBA during the day and 45 dBA on quiet nights. I don’t have high-sensitivity speakers like 95 dB/1W/1m. To hear my system well at 45 dBA, I need to perform room correction and EQ. The end results are pretty close to the ELC (Equalized Loudness Contour) human hearing perception level at nominal SPL—everything is dialed in. Bass is articulate, tonal balance is right and life is good.

Interesting discussion. 

On my system, it sounds very good around 60db, that is usually my morning listening volume while the house is asleep. The sound is clean, clear, good soundstage, good dynamics. 

When I turn it up, it does get louder, but it does more than that, the soundstage gets much bigger, everything opens up, get better imaging, with the bigger soundstage, much more presence. Everything is clean, more clarity, better seperation. The music has weight to it. You can feel it pressuring the room. This works up to around 100db.

Over 105db, it's still clear, but starts to hurt being in the room, the soundstage is much bigger than the room. But there is no distortion, you can still pick out each instrument. Mids do start to get a big forward, the highs can start to get harsh. Bass however is glorious! The whole house starts to vibrate. At these levels, the treble control goes from 0 to -4 or -6, to tame the harshness. 

The sweet spot is around 90db at my listening spot, everything just goes tougher. 

As an aside, I noticed that the Sound Meter app running on my Pixel appears to be throttled at 80 dB, meaning no matter how loud the music is the app flatlines at 80 dB although the display itself goes up to 100 dB.

Last night I was listening at 70% volume and the app showed 80 dB although it felt considerably louder. I had to turn the volume down to about 55% before the app showed anything less than 80 dB 

Wonder what’s up with that

Floyd Toole is a pioneer and a scholar in sound reproduction. I'll go with what he says. Do yourself a favor and explore his work and that of Earl Geddes.