Comparing a Yamaha s301bl to a rega elicit mk5 - a/b on some paradigm 800fs and they sound the exact same. Looking at the specs it makes sense - I don’t know why I’d ever use the full wattage of even the Yamaha without getting hearing damage and the THD being 0.019% vs 0.004% makes no functional difference. Are high end amps the new snake oil? What exactly are you getting for 10x the price here (besides the rega having less features and the rega brand name?)
THD isn’t everything - what about resistance to voltage fluctuations, RFI, damping factor and rising SINAD with lower impedance/reactive speakers?
Those things are harder/more expensive to control and might explain some of the differences between good and great even though you may not hear it in most situations.
People running electrostatics and low impedance speakers may push lesser amps into areas where they aren’t so pretty sounding.