Decisive Battles

[Frank]

As for Teutoberger Wald, I can see it as big, but not really decisive. The Romans didn't conquer Germania, but they maintained control of that area with the Agri Decumates and the Frisii anyways.

Actually, there were much more tribes allied with Rome during Arminius coalition and afterwards, e.g the Chauci and the Hermanduri to name just two of them.
Of course the romans tried to maintain control, but with a different strategy. They changed from provincialisation to a kind of client-state strategy. Latest with Claudius adventure in Britain and the later measures of Domitian, this strategy started to fail. The romans were far away from controlling any strucutal changes in Germania Libera afterwards. And the consequences became harsh starting in the 3rd century.

Looking to the Pax Romana, you proposed alternatively, I have a different understanding of this term. For the romans the Pax Romana started with Augustus, even if his legions expanded the empire more than any other emperor after him. Pax Romana means peace amongst romans after these terrible civil wars. And has not that much to do with provinces or barbarians from a roman point of view.