Oromo were squatting in the north and assimilated hararis/afar/somalis etc during the adal civil war, nobody would confront them until Somalis started organizing themselves and pushed them out. Many Oromo converted to Islam and were not seen as an enemy to the adal state. This is why their migration wasnt viewed as something that needed to be stopped. The Habasha threat was greater. Adal, when it was Harari only, also faced a Somali/afar migration, therefore oromo did not do anything that wasnt new, everyone migrants at some point in their history. Oromo are only made fun of because they were the last to do it.
I was agreeing with you until you said Adal was Harari only when it also composed with nothern Somalis and Afars. You need to cut with the Harari supremacist revisionist bullshit. Adal only faced Oromo expansion so that's another lie you stated.
These are Ethiopian sources so go read it. Even they are more honest.
Here: https://books.google.co.uk/books?id...Ifat Sultanate was a Somali Sultanate&f=false