Harla was the term used for the farming/urban population of the north, they were kinda like RW. Again ethnicity wasn’t solid in this period so Somali speaking farmers and Argobbas were both called Harla.
btw the Somali peninsula was majority urban until after the Adalite wars.
nomadic dominance happened because of a dark age, so calling them somalis even though they spoke a language that Somali is descended from wouldn’t be right,
Somalis (as in nomads) were marginal and only grew because of the cities being destroyed and their inhabitants joining them, and the land becoming less green.
see
Ruined towns in Nugaal: a forgotten medieval civilisation in interior Somalia
S. M-Shidad Hussein