I don't understand why nobody appears to have grasped this yet, as we have??
I fully understand you points, and they are valid.
If I found a Bryston amp for reasonable money, I'd love to try one out.
Is it 1% (or more) better? Very likely.
I use a Crown K2 amp in my basement and it sounds outstanding. Is 1% better going to make a difference to me, likely not.
But you are correct, 1% better is still better by definition.
Why folks don't gravitate to the more expensive (but better) power amps, is that it's a point of diminishing returns.
When we're blessed with something like the Axe FX, sometimes we can 'cure' other component deficiencies right in the box.
If my power amp isn't totally flat, maybe I can cure that with a little Eq.
Don't get me wrong, take an old Behringer power amp and throw it up against a Crown reference amp, and you will hear a significant difference.
Some of that graininess with the old Behringer amps will not be solved by Axe FX tweaks, and it can't/won't sound like a Crown reference amp.
Some people can live with that, some people can't....and of course, budget has a lot to do with it.
Some people are super happy with a QSC CP8, and some people are not happy unless they're playing through an RCF NX12ma.....the power amp conversation is the same.
My old studio engineering instructor (Dave Moulton) designed a nice Bang&Olufsen speaker that was the perfect studio monitor. I've never heard music sound as good as it did out of those speakers. But they're $15k each. Although I know how much better they are, I'm not going to buy them.