Lots of really good content here. In my opinion, there are definitely several factors, besides the more obvious speaker load, room sizes, listening levels, etc.
Current can be very important and power supply design is a major factor here. I am not of the mind that more power is always better, particularly within a designer’s range of products.
i have a Pass XA25 driving a pair of Dynaudio speakers in a decent size room (though I do only sit about 8ft from the speakers or so) and for me, the Pass may have run low on steam once.
Many, many moons ago when I worked in a high end store, it was not uncommon for one company’s lower wattage products to have some qualities that bested their larger wattage amps. Sometimes this was timbre in particular, but sometimes soundstage as well. Bass control on larger speakers does usually require more wattage.
Now with very sensitive speakers and very low wattage tube amps, that is a different thing of course…