restorer-john
Grand Contributor
...What's stopping amps from much heftier power outputs at clean levels?...
Lawsuits.
Consider headphones are >100dB@1mW, yes ONE thousandth of a watt. You simply don't need power of any significance for headphones, just an ability to swing a suitable voltage over the impedance of the cans to give levels that aren't in firmly in permanent hearing damage territory SPLs.