It is the different strains of arabians that exhibit different degrees of the jibbah.
The different tribes bred different strains and some have a very pronounced jibbah and others a straight profile.
The arabs did not believe in crossing the strains. So different regions had horses that were different sizes, colours, and degrees of the dish.
Though I do not think the extreme dish we see in the show ring was prominent in the desert. Shalom
Yeah, that sounds about right. Bedouin are pretty careful about keeping track of their own linages, those of their camels and horses. The linages of camels and horses are associated with certain groups so that they know the family tree of the animals as well as their own, spanning generations, and many groups are well known for breeding particular types of animals. For example the Al Murrah Bedouin of the Rub alKhali in Saudi Arabia are well known for breeding very expensive black milking camels (which can sell for over a million US), some Howeitat Bedouin from the south of Jordan are famous for breeding pure white camels that are highly valued for producing very fine wool, others in Egypt were known for producing enormous draft camels that were highly valued for many of the Bedouin who were involved in smuggling between Egypt, Saudi and Syria up to about the 1980s, and there were many tribes or sub-tribes throughout west Asia and north Africa who were famous for producing valuable racing camels too. It was the same for horses, as far as I can remember the Rashid, who were powerful throughout Nejd and the Hejaz, until the Sauds beat them and established Saudi Arabia were famous for their horses, as were many others.
But, given that Bedouin tribes are fairly anarchic in their operation with very little central decision making processes that could have shaped a unified breeding programme, and, though major linages of camel and horses may have been in the hands of maybe a sub tribe rather than a whole tribe, which could have given some measure of unity in breeding, the animals, or the whole breed, would have usually been spread across sub tribes of many tribes given the practice of raiding and the prestige involved in seizing the animals from other tribes, I'd be guessing that there would be a reasonable amount of variation in characteristics that people would have been breeding for.
Still, from what I can recall from reading Blunt's books, she noted that back in her day that some breeders were digging the dish head, mainly in Britain and Europe as far as I can remember; she seemed to be a bit critical of the practice. But it wasn’t so prominent in Nejd, and maybe Hejaz. But if it was becoming a thing even back in her day it is certainly something that has been thought to be a major breed characteristic for a very long time. But then it was a while ago that I read her books; my memory might be a bit hazy.