>>511378667 (OP)The main reason the Romans didn't conquer Germany is because Germanicus was betrayed by his own people and not allowed to achieve his true potential.
The same reason as to why the Romans managed to conquer the Lusitanians: Viriato was betrayed by his own people and not allowed to fulfill his destiny.
Merit in the battlefield is secondary to these things. What determines success is first and foremost whether or not you have traitors in your ranks. The #1 enemy is the traitor.