To answer the question posed- if I were advising or looking for a horse to do hunters/jumpers, the DHH is not where one that would be at the top of the list. That is just not what they were bred to do, and that doesn’t preclude the one-offs that have suceeded. Just like the Arab who placed at PF. The conformation of the DHH and what they were bred from and for, is not what easily translates into " natural jumping ability" as a whole breed.
Yes, we can name a few. If they excelled at the sport, you’d see much more of them.
I am all for " I love this horse and he does the job and is happy". Have fun, enjoy the horse you have, hopefully the horse enjoys the job. My point is- choose wisely if you are choosing to do a specific discipline in which you want to excel (and your enjoyment is contigent on ribbons). You can generally ride almost any horse in any discipline, and enjoy it, but not necessarily excel in competition. (depends on your goals and definition of success).