For what it's worth, i have over 11,000 Watts in my 96 sport Jeep Cherokee. 8k going to 2 18" subs, and 3k for Mids and highs, 6 8" mids and 2 super tweets. Rms, not peak wattage. My Jeep sounds extremely musical, no distortion. Point is, high power =/= distortion.
I realize that it is possible to have power and great quality sound if all the components are of high quality and they are matched well. That is what Apple should have done. Sound should be balanced on iPhone X at all settings. If the speakers can’t handle that max volume, then lower the max volume via software.
MacBooks already do this and there are apps out there that push the speakers to their Mac albeit at the cost of distortion.