My problem was with the simplicity of your analysis regarding Rome's management of conquered peoples. I've seen others try to "boil down" Roman history and I have to say something...
Like I said, the real reason Rome gave up on Germany between the Rhine and the Elbe had more to do with economics and the Will of The Senate. If grapes, grain and olives(or fish sauce...) grew in Germany as they did in Spain, believe me, Rome would have stayed. There wasn't enough of a ROI to keep several legions there, traipsing around the German countryside to keep the tribes in check.
Dacia and Dalmatia on the other hand did have an economic incentives, having gold and other minerals, as well as grain growing capacity. Also, Dacia was more of a military threat to Rome than the Germans, as the Dacians were more organized militarily than the German tribes. Germany had slaves and wood and some lesser mineral wealth. Both Dacia and Dalmatia had similar/geography terrain(especially Dalmatia) to Germany, BUT, had a better ROI(at the time, 1st centuries BC/AD.)
So my point is that the Romans would and could defeat and manage a people, regardless of culture, if there was an economic or strategic/military reason to do so .
At the time, "owning" the Germans wasn't worth the trouble, though I'm sure they wished they had done it, looking back with hindsight from the fourth-fifth centuries.
I would recommend any books on Roman history by Adrian Goldsworthy and Anthony Everitt.