The first thing that discredits the DIR theory is we would need to accept the same people occupied the same land since the 13th century without any shift, migration, disease, war, or climate change occurring. The fact climate change is so common in Somalia, shift of population would be required at least every 50 years, let alone 800 years.
The liklihood of the same people populating Zeila over 800 year period(14th century to 21st century) is ludicrous to any logically sane person, it's not even sellable knowing how migrations happen in Somalia due to wars, diseases, and climate change such as droughts. The fact Somalis MOVE every 50 years is most likely scenario. So are u arguing DIR have been inhabiting the same land for 800 years without any shift of population? Heck Bah Dubays just shifted within 20 years from Garowe to Birta Dheer and we Shifted from Qardho to Garowe all over 150 year time period. You can imagine where my clan will be in 800 years.
To argue no other older population be it(arab or harari) didn't exist in Zaylac PRIOR to DIR is ludicurous. The other thing that hurts that theory is DIR are nomadic not COASTAL settlers, what the hell was DIR doing in Zaylac? heck even Bosaso is known to be ARAB as xafatul arab is the oldest settlement in town, infact all coastal areas have proven the oldest quarter are ARAB, not Somali. Somalis are just camel helders in the interior nothing more, they don't have coastal civilization till much later like 17th century
