Why would anyone want class AB amp when class A always sounds better ?

Miller didn't say a bad word. If he wants to sound right - fine.
Going too far into the subjectivity will get us nowhere.
I mentioned D'Agostino class AB amps as being more than competitive.
Maybe his class A amps would've sounded even better. I bet, he didn't want huge size and heat, so he opted not to do it.

I can chime in on this. I owned a Plinius SA-103 @ 220w into 4ohms which is class A biased driving a pair of Legacy Audio Focus speakers @ 95.4 db sensitivity. I always felt like it lacked power. Indeed, there were certain passages where I would drive it to clipping. One of which was Loreena McKennitt’s vocals on the Dante’s Prayer track from the Book of Secrets album. I decided that was unacceptable and that I needed more power. I sold the SA-103 and purchased a SB301-MKII class A/B which is 470 watts into 4ohms. The difference was amazing. I had all of the great Plinius sound and none of the "lack of power" issues. The bass was driven with much more authority, the highs were crystal clear and well defined. I wasn’t quite sure what to expect but now I wouldn’t trade my amp for anything. YMMV but in my experience the additional power of the class A/B amp trumped the class A hands down.

BTW, I do have a Coda CSiB for sale if anyone is interested.

I am sure George and some others could offer an explanation of what happened beyond just formal power ratings.
I like Loreena and Dante's Prayer track is one of her very best. 

I am sure George and some others could offer an explanation of what happened beyond just formal power ratings.

Here we go, watch out for the flame throwers !!

Stereophile: Legacy Focus
Not only are there two minima in the bass of less than 2 ohms, and another of less than 3 ohms in the mid-treble, but there is an amplifier-crushing combination of 3.3 ohms magnitude and 60 degrees capacitive phase angle at 20Hz. Fortunately, it is rare in music to have high levels of energy this low in frequency.

They Legacy’s might have been 95db, but they were a "savage load" for any amp right through the bass up to 150hz, 1.8ohm load with 40 degrees of - phase angle 55 at 30hz!!! that could simulate lower to the amp in the bass
https://www.stereophile.com/images/archivesart/LEG20FIG1.jpg

Especially bad for complimentary push pull Mosfet amp with a lot of A bias they don't do current very well into low impedance.
Bi-Polar amp (BJT’s like Ago, Gryphon, JC1 Krells would have far better with these sort of speakers)

And what looks to me like a "average amount" of storage reservoir capacitance for a Class-A especially, may have the watts, but looks like not much for reserve for current. Sure it got 2 trannies but where’s the massive stack of power supply caps
https://ibb.co/3rZbwdm
https://ibb.co/zF89tFR

Cheers George