There has typically always been a Reer Waqooyi and a Reer Koonfur dialect/accent. There were then subsets of that.Bosaso is technically more north than Hargaisa, politically Bosaso is looking to Mogadishu but that can be said about Buhoodle as well. the culture argument is fake news, Somali culture has small variants perhaps it can be summed up in differences in accents and Bari has unique Rer Bari accent, there is no common southern accent, unless you think all the south sound like Rer Xamar.
I bet if you were to look at things like where our words for things differ, people from Bosaaso, Garowe etc. have more words in common with Muqdisho folk then Hargeisa folk.