Before the smallpox epidemic, there was no substantial conflict as the first set of migrants came seeking sanctuary among the Galla after the Rahanweyn pushed them across the river.
View attachment 217992
View attachment 217993
If the status quo had not changed because of disease, and later guns,
what makes you think that these migrants would have been more successful than the Rahanweyn led Gasargude Sultanate and Bardheere Xeer who could call upon ten times more warriors at arms? There would have been no need to become clients of the Galla if their manpower was strong enough to defeat the Rahanweyn who they first came into conflict with.
Moreover, both the Gasargude and Bardheere Rahanweyn dominated entities were already successful at dislodging the 'Galla' from territory as the above source highlights.