You are quite right but for me the preference for a lightweight Class D head comes from necessity, I can no longer hump two large lumps of iron around at close to 69. So yes that puts valve amps out of the question. I love my old HH amps but they were designed to sit on top of a 4x12 and my cabinets are smaller than that. Even the best Class A/B amps (ABM) overhang my current cabs.
I think of it like this. If I were a mechanic, I would use Facom or Snap-On tools, but for me my Lidl spanner set works, has never let me down. The same goes for my amps, The Bugera Veyron has never let me down and is manageable and does not look silly on top of my cabinet. Another point, modern cabinets are smaller. It made sense for big wide amps when sat atop a cabinet 2ft6 wide (750mm approx). Newer cabinets tend to be designed single or vertically aligned speakers as speaker design and drivers have evolved.