From what I’ve read here no one is comparing a well designed class A/B amplifier against these class D amplifiers. You cannot say that switching power supplies in these amplifiers are better because it’s simply just not true on paper or to my ears. I’ve heard lots of class D amplifiers over the years and even the most recent and it’s always missing something.
Indeed class D amps with switching PSUs miss a lot compared to Class AB amps with a linear PSU, and even more so wrt Class A amps: cost and the power bill. In fact KNOWING that the former are much greener makes you AWARE that they must sound worse.
Note that switching and linear PSUs can ne both used with Class A, AB and D amplifiers. They are not “tied”. Indeed, one of the best measuring and sounding amplifiers in the world, the Benchmark AHB2, has a SMPS and class AB circuitry (and, to audiophile horror, a type of feed forward circuitry designed by THX, which means that it cannot be good, right?). There has been significant praise for Tom Christiansen’s Modulus series, and you can either use a switching or a linear power supply with them – in the listening impressions there has never a bias I could notice depending on the power supply type.
FWIW, a few years ago Austrian and German audiophiles and DIY enthusiasts have met in Munich and there was a blind shootout between a 300B based triode (designed by DIY authority Manfred Huber) and a UcD 180 build: the majority thought that the latter sounded better and therefore had to be the Class A SET 300B build. The report can be read
HERE.
I am quite sure that in a blind or even double blind test you would not find that a recent Class D build lacks something.