Well yeah. Even 19th century Race theorists believed Somalis to be the Cushitic group to have retained most of their original make up. Amahars and Habashi are recently mixed with Arab (New West Asian)
Using Somalis as a proxy for Cushitic makes full sense
What do you mean "the similarities that they found they couldn't explain away?" If you mean differences, then there is really no need to explain why Amharas and Habashi are recently mixed with Arab as that is documented and also easy to spot. (They're lighter and shorter on average, with higher frequencies of kinky hair, which didn't come from Arabs but most likely Omotics/Nilotics/Some other group.
And again, even the white 19th century Race theorists believed that the original Cushitic stock that Horners are descended from were tall, narrow faced, narrow bodies people.
Still want to point out that I hate white race theorists and the ideals they tried to force upon everyone, only using this for context.
Context for what you may ask?