Yeah I think I might have seen that post about how there was even a somali sultan of one of these towns who fought with the tahirids or something. I once a twitter society listened to mohamed artan mention that there are somali names appearing in biographical dictionaries in the 8th/9th century. We have obviously had an old scholarly tradition. Their gonna publish in the coming year with looh press the phd theis of a somali guy who studied in azhar in the 70s in which wrote about where somalis appear in arabic primary sources.The MSA languages are not descended from the OSA languages, no. Weird, I know. They should have maybe picked a different name, kekekeke. But they interestingly do have a Cushitic substratum, that appears to be legit. That same linguist I knew confirmed as much years ago as well. Yemen is also littered with the same ancient Cushitic rock-art as the Horn that begins to appear around 3000 BCE and ostensibly comes from the Sudanese Neolithic. This rock-art is found enough in Yemen that some scholars call it the "Ethiopian-Arabian" style of rock-art or something to that effect. All most likely left by early Cushites. I lost the paper but about a decade ago a Tigrinya friend also showed me a study showing Horn to Yemen archaeological influences even after this in that Horner stelae culture also spread to Yemen. It was definitely not always a one-way street influence wise. Yemen seems to have possibly been Cushitic before the Semites came from the Levant and supplanted the earlier Cushites.
Then there's also the fact that, historically, despite how much people try to ascribe Arab origins and dominance to Somali port-towns it was historically Somalis who had a far stronger presence in Yemeni towns like Mukha/Mocha and Aden whereas any descriptions of Somali port-towns from 1300s to the 1900s mostly give you the impression that anyone "light-skinned" or outright recorded as Arab was a very small minority. I wish @Idilinaa was online. He had a lot of cool stuff about Somalis being in Yemen as far back as the 1400s-1500s that he showed me ages back where he convincingly showed, with scholars like Shidaad, that the people being called al-Jabarti or al-Zaylai'i running around Yemen back then were basically Somalis. But point is that Yemen to Horn influence didn't always go that way. As you know, the northern Xabashis literally once ruled a part of southern Yemen.
But that being said, MSA speakers are actually a very interesting bunch in that they seem to have maintained a system similar to Somalis during the Early Modern Period of using Arabic as their written and trade language in many cases then their own mother-tongue (i.e. Mehri) to speak amongst themselves. Though, if I'm not mistaken, unlike with Somalis there's not much proof of a tradition like Far Wadaad among them until very, very recently. They seem to have overwhelmingly used Arabic and perhaps also OSA in the past to write, though I'll do some more digging sometime.