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People like you are really needed in this day and age. You sound really educated. Cerulli just writes down what he hears and everything he heard is based on oral history. Nothing factual.The custom of cutting parts of the children's hair was not a "Shirazi" introduction. It was a chief ancient Cushitic practice and extended to East Sahelian non-Cushitic peoples, that likely got it from Cushites. More like random Hawiyes guessing and making up stuff instead of it being an oral tradition and Cerulli leaning on those fabrications.
I have read mentions of old, now conveniently gone fragments of structures made by supposedly Iranian-speaking peoples that today cannot seem to exist anywhere near the southern coast. I think it is worth an investigation on archeological grounds, and conceivably more evidence of foreign contact will be uncovered in the context of the ancient trade, things we know took place.
One needs evidence and firm multi-modal substantiation for extending influence from southeast Africa to the southern Somali coast. If Southern Somali contact with Iranian types happened, which I have no issue with (besides the weird affinity to state that West/Central Asians came to the coast first), it would likely be a separate thing from the Swahilis until that is disproven by facts on the ground.
No doubt the entire region all the way down the Azania coast was inhabited by Proto Somaloid groups. I’m guessing they were the ancestors of some of the E-M293 Somalis we see today in the south. This also might include the E-V32 Kenyans we see as well as the linguistic connections with Rendille, boni, aware, girirra etc