No fabricated/incorrect lineages would appear, people would identify with their region and faith. More solidified and developed language/writingwith maybe our own script or writing system. Population would be much higher. Less dialects. Possibly develop advanced civilisations like other horner farmers did, Aksum, Adal, Lasta Kingdoms, D'm't, etc. More Somalis would benefit from foreign trade rather than having trade being monopolised by just certain clans; the wealth would be distributed among the cities and communities.
Disadvantages would be that if a foreign force arrived then slavery and oppression would be rampant. The reason nomadic Somalis were able to dodge this was because it's much harder to enslave and control nomads. They live at long distances away from each other, aren't good at physical labour, and they can easily/quickly move or run away to certain areas. But when a city state is invaded it's screwed unless u can defeat invaders in battle.
The Bantus were smart for grabbing farmlands in Somalia.