I own all three breeds. Tough to generalize as there are strengths and positive aspects in each breed. Specific to my experience, the warmblood breeds carry less tension in the backs which allows them to climb the training ladder quicker than a horse with a tight back. Confirmationally, the Arabians & TB's can have a straighter gaskin which can challenge the horse's ability to sit in the very collected work. - it take such an enormous amount of strength to piaffe, passage, and pirouette - some would physically break down if asked to do this level of work on a regular bases. (It's hard enough keeping them sound at the upper levels, never mind if physically they aren't built to do the work!)
But that's just the confirmation piece. TB's and Arabians have fabulous work ethics and hearts the size of TX. I find the WB's think a bit "me first" but even that attitude can be re-directed into "ego" and they want to please because they want to show off.
Anywho, I have been lucky enough to have ridden all of the various no-no breeds, as well as the shoulda been a yes-yes, but wasnt LOL
The rider really does have to stay out of the way of a horse to a incredible degree at the upper levels and then adding to that if your horse is not naturally balanced and uphill even you are required to be a frickin statue
Whenever I get on a horse and notice that my errors are tipping the scales so often it can be discouraging and so I advise anyone who can throw their horses balance off again and again and again while they are trying to learn to try something a little sturdier...
In the mean time -
Arabians everywhere are teaching their riders how to transport through time and space, while Tb's are showing theirs how to ride through time and space and back again and one more round... Are you still up there? Oh goodie, one more round at mach speeds!
Wb's everywhere are putting up with mistakes until they wake up long enough to throw their butcher handed ammy like a lawn dart!
Honestly these guys all teach us so much... If you own a Wb, go ride an Arab today! Tb people do the same! Arab people get up on one of those jumbo jet wb's and feel the earth shake a little! (wear a good bra tho)
Im all about riding whatever will sit still long enough to leg up on! It hasnt changed since I was five