Even Ibn Majid who lived in the 15th century(the same century as Yeshaq) casually talks about Barr Al Sumal in his book like its some well known country opposite Barr Al Arab@Idilinaa Is it not possible that the etymology is So'maal (i.e meat-workers people who live off their livestock)?
Do we have any potential explanations for the legends surrounding Harla- i.e they were arrogant and so were destroyed?
Is it not possible those Harti Suleyman were considered 'Harla' then if we take it to mean just a settled agro-pastoralist Somali?
I have also seen a new source the Yemeni historian Hassan al Khazraji mention an 'ardul Sumaal' in the 1300s when talking about where a Shaykh Abdullah al Jabarti died so it seems like the name was established before Yeshaq I mentioned it in his victory poem.