Could you please explain to all of us how centralized the HRE was?
The HRE was the most highly decentralized state of its' time, particulary from the 1500s onwards. It consisted of up to 350 states,each of whom owed allegiance to the Emperor but were de facto almost independent. Which meant that they formed often alliances with foreign powers against the emperor.
Yes, diplomacy was never Germany's strong point
History tells a different story, Germany has prdouced some of the finest diplomats of their time. Frederick the Great, Metternich, Bismarck...
And later the chancellor's of the FRG achieved some significant diplomatic achievements. Adenauer's redemption of the FRG in the West, Brandt's Ostpolitil, Kohl masterfully handling the negotiations for German reunification. Merkel herself showed great skill in handling the Euro crisis, brokering the Minsk II peace agreement and now with the coordination of a European response to Corona.
I mean no offense, but when I think about a country that has a historical lack in diplomacy I think of Poland. Over the ages Polish leaders haf a strange fixation in leading their country in diplomatic isolation, with PiS following this tradition.