One thing nobody has mentioned so far...nowadays, the training for these highly specialized competition is sometimes close to abusive, and an Arabian will not, due to his intelligence, take that kind of training very well. And rightfully so.
All myth! Good trainers can train them for about any event and they will try and work their hearts out. I knew an Arabian Cutting Horse trainer for many years named Tom Miller. I even bought an Arabian mare for him and used her for a broodmare for many years. His cutting horses tried as hard an any horse I ever saw. They just were not competitive in the bigger NCHA Shows. He DID WIN some at the local level in NCHA competition. -- like the better Arabian barrel horses I knew.
I certainly do not consider event training to be abusive. You find abusive trainers in all disciplines. Arabian just get completely crazy when they are abused much like TBs and racing QHs. They are just more thin skinned and sensitive and some of them do not have good enough minds to take a lot of pressure. There are Arabians that do nothing well other than halter just like there are QHS that are ONLY halter horses.
I used to laugh at people that could not get along with 'hot' horses or mules. I used to tell them that the first thing you have to do to get along with sensitive and super smart animals is you have to be smarter than the horse or the mule.
And "Yes!" All 'light' breeds can trace in part back to Arabians. They have long been called the 'fountainhead' of light horse breeds.
I have never 'bashed' Arabians. I like them, have raised them and have trained many of them. I am just realistic and know what their strengths and weaknesses are.