Are we speaking anthropologically ? then I would say Dir is the pure Somali, if we speak in terms of identity then I would say purest Somalis are from the interior, Doollo/Hawd/Gaalkacyo/Burco/Caabudwaaq. DNA of population, I would say Dir are the least pure, they mix heavily with all sorts from Jareers in Jubaland to Oromo in Kilinka.
most Somali have DNA 99% Somali but this will change rapidly in the next 10-20 years, due to relocating to bigger cities as well as coastal cities, not to mention the massive Somali diaspora that mix with Jamaicans, Chinese iyo balaayo oo dhan.
All Somalis that live in the Oromo frontier possess genetic influences from the neighbouring Oromos, especially the ones who expanded by force. For instance, the Waamo Ogaden and the Guuri MX would breed with captured Boran and Wardey concubines.
Furthermore, no Dirs in Jubbaland openly breed with Bantus. As their former slaves, the Bantu identify with the clan that owned them. Hence, why you get Geledi Jareer, Wacdan Jareer, Biimaal Jareer, Moblin Mudulood Jareer. There might be individuals that get jungle fever, but there is no tradition of marrying former slaves among the clans that historically owned slaves in the Jubba and Shabelle regions.
Lastly, Somali identity is patriarchal, you are who your father is. Dirs are not any purer by ancestry than other Samaales. If you belong to the Samaale Family, you are Somali by default irrespective of who your father humped.