No one said TB should not be bred into sporthorse at all. What is usualy said is that TB usually compromise the jump for the first generation, but the qualities will follow along in the next générations. Even the greatest of advocates of breeding thoroughbred in europe say so.
I just find it amusing how people find all sorts of excuses as to why we do not find as much thoroughbred in the sport today as we did 40 years ago. It is, however, the first time I read that the modern courses are built to “accomodate” the warmbloods. The courses evolved because they could not go any higher. They became much more complicated. It is not because the jumps are not as high that it needs less power. Jumps in today’s courses needs to be jumped in any angle, and often at any pace. WB breeding evolved into that direction and they kept excelling in the sport, even as it has become today.
It is not the riders inability either. Most of the riders learned to ride on thoroughbreds. The thoroughbreds are not such a particular ride, impossible for the europeans to understand! I it is good, it is as rideable as any other horse for the good rider.
Finally, I do not believe in the fashion excuse neither. Maybe in the lower classes, where people want the big, eyecatching ride and they have the money to buy it. BUt as you rise into the higher levels, the horses are getting rarer and good horses will find buyers. We still see TB in lower level, but somehow, they do not seem to make into the next level.
I would just submit an idea. Maybe the TB are not bred as they were 30 years ago? Breeders in Europe are always looking for the good TB stallions to bring into the studbooks. I have never heard any credible breeder saying that their is to much TB into breeding, or that we should avoid TB at all costs. However, they almost all say that they no longer find the Lady killers, Laudanum, Hand in Glove of Furiosos today.