Did somalis as a nation exist before islam? Very likely At the very least we know our neighbours in the arabian peninsula saw us as one people. How can we determent if somalis saw themselves as a single ethnicity?
Well first off let's just look at clans rather than the name somali. The primordial clans of somalia that existed before islam are samale and sab. Samale with the sagal samale and sab with digil iyo merifle. Any other clan aside from them claim arab origin, well even these two clans sometimes also claim arab origin but usually they see themselves as somalis rather than arabs.
Almost ninety percent of somalia was inhabited by samale before islam meaning a single clan and a single family. Any other clan that claim arab origin married into the samale family to became somalizised.
It's either marrying into dir or into hawiya and at times into the sab family. So yeah you could say in a way that a common identity existed before islam and these people also to a large part also spoke the same language with different dialects.
Russians were seen as one people before their ethnogenosis under Rurik despite being divided into different mutually unintelligible languages like
Merias,
Veses, and
Krivichs and Chuds.
Also mythologically Samales real name was Cusman and he was a Muslim, the people who lived in Somalia before Somalis were destroyed by Allah while he slept in a cave. We all know that Saab is a myth, Digil migrated into Somalia from what is now Arsi land after the oromos invaded them.
also how the hell are you arguing that “90 percent of Somalia was inhabited by Somalia” when the first reference to the word Somali comes from the Abyssinian hymn after their defeat of a Muslim kingdom in Ethiopia literally titled “Go Tell The Somalis”.
there’s no exclusiveness between claiming Somali origin and Arabic origin, all the noble Somalis do so, it is like the Poles claiming to be Sarmartian or the Irish claiming their ancestors came from Scythia.