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

Once again

You can prove this for your self by listening to an amp with user switchable bias while listening. EG Parasound JC1(low/high bias), Gryphon Antillion (low/high/higher bias) etc etc.

The difference you hear with more/higher Class-A bias, is an easier, smoother, richer presentation to the sound, that’s no less dynamic and yet makes the speakers disappear, even as the music goes louder. And as a result the sound washes over you rather than being fired at you from the drivers, and that is the result of the lessening of the class-B xover distortion when you engage more and more Class-A bias.

Cheers George

Ralph - Let me know if you need a Beta tester, I can pay the freight both ways. My systems are visible in the virtual systems page. I appreciate your balance of the theory and practical application ( the hard work of design ) I also appreciate that you understand the ear / brain sensitivity to and preference for certain types / orders of distortion. A deep understanding of that can greatly inform the design objectives for any amplifier.
jim

People with blood type A are always better than ones with blood type AB. What???? A nonsensical statement but assured to arouse a response.

Class A runs very hot and very inefficient , big watts in pure class A is big bucks

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And when one's listening room is located in say Here in New Orleans, or Phoenix, or  South Florida, , the heat factor of a  class A amplifier is a  important consideration.
 The  Defy7 is like, I think Richard Gray says more like class B,  throws off  less that I had anticipated/with 12 tubes. 
, Richard also prefers Class A.
 But as you mention, Big Bucks. 
Did you say very inefficient?
Oh I see , requires plenty of power current = heat.
Glad the Defy is not class A. the heat  radiation would be too much to deal with in my 10x12 listening room.