No, there will be another group introduced, later on, that's the equivalent of the steppe tribes. Hell, they are even semi-nomadic.
The Germanis people are meant to be Northern Gallic and/or Southern Germanic people who were decent horsemen, but not the best. If you are looking for an example of Gallic/"Germanic*" cavalry, look no further than Caesar's on "Germanic*" Cavalry.
* North-Rhine Gallic, but called Germanic for propaganda reasons.