Interesting link you posted, this this is more of a side discussion and not really that important to the point I'm making, which is arguing against their self-perceived autochthony in Somalia. Exact admixture and how much of what they have varies widely.
Still, the fact that South Asian, to use a more correct term, is still the biggest or second biggest, being neck and neck with MENA, (which has both Persian and Arabian admixture put under one umbrella), non-Somali heritage they have is a interestting pheneomena that in their and our oral history has never been mentioned. Their ancestoral merchant ancestors might have done some rebranding by claiming to be from Yemen, which for many clans is their
mythological ancestoral land, to better fit in. This is just speculation though!
You are right, though. Somali DNA is now by far their biggest genetic heritage and will continue to be until their genetics assimilate to the point of not even being phenotypically distinct from Somalis.