I won't go into the usual discussion of stupid or not stupid, trainable or intelligent and all that.
But I would like to tell a little story.
I used to board at a big equestrian center, 120 horses at any given time. Standardbred s, jumpers, and what not. I was the only one with Arabians, I had three. My paddock was the last, about half a mile from the barn. So I took my trio out together, one left, one right, one behind me. We had to pass a good piece of the track, where the standies were training, then along the jumping arena, to get there, and back to the barn.
One evening I got my trio, we headed home, came up to the arena. Next thing I saw was a huge white horse flying over the arena fence, getting hung up, summersaulted and ended up on it's back, right in front of us. Each of mine were about 17 hands high, snorting and blowing. We passed. Passed along the track, horses doing fast work, 5 of them, only a hedge between us and them. Again, 17 hands high, snorting and blowing x 3. Then a bunch of kids on bicycles, waving plastic bags and screaming and yelling. And again, 17 hands high, snorting and blowing x3
We arrived in the barn, everybody went in his/her stall, I took off halters, closed the doors and had to sit down for a moment........not ONCE was there any tension on the leads, not once they tried to get away from me or even ahead, no kicks, no bumps, nothing.
I'm convinced I wouldn't have survived that with any other breed.
One of them, super-hyper-sensitive, more than once got me mad because he would act up for no apparent reason. Only to learn later he aways had a reason...a lose horse behind us or in the arena, a rider in trouble or such. He also never forgot the white horse falling out of the arena. Whenever there was a white horse going faster than a walk he'd get uneasy....for years.