This is a muse, take it for what it’s worth.
Perhaps I’m wrong, but in breeding anything you have priorities. No horse is perfect, so you breed for qualities that suit an intended purpose. Having ridden many a WB “meant-to-be-world-beater-but-didn’t-make-it” I would argue that they are not well-matched to the average amateur. They were not very fault tolerant and while trainable they had too much energy and gait for the adult amateur dressage rider who, let’s face it, tends to be an over 40 year old woman with some arthritis and a desk job. I’m not knocking us - I belong here too with my injuries and I could not ride the horses today that I could ride 20 years ago - I’m just saying, most of us need something that is quiet first, and athletic and flashy belongs way down the list.
Quarter horses do this fairly well, as someone mentioned upthread, the cutting horse lines tend to be full of zest and athleticism and the western pleasure mounts tend to be much quieter and “born broke”. But QH’s do not do well with many recognized dressage judges, because of the gait factor, driving many amateurs to western dressage.
I think this trend is noteable, as the quality of the WB and the gaits have increased to meet judging standards, they have become less older broken amateur-suitable just by virtue of athleticism EVEN if they are pure gems from the temperament-standard.
It’s an interesting issue and will be curious to see how it all evolves.