I disagree! Alemanni could be used against Romans. If Augusta Vindelicorum is destroyed by our king Visimar then Alemanni have a chance to expand south. Perhaps raid even Italy! This could've bought us more time and Romans would've concentrated their war efforts against the Alemanni and not against us!
Also, your reasoning "if we don't kill them, other hordes will" is not very good one. If we kill them now then we make it easy for others to follow us and then, when we are tired and small in numbers, attack us.
I heard from some travelers that Huns and Sarmatians are still fighting near Sarmatian capital camp.(OOC: There is a huge black land near the place where Sarmatian town should be.)