My learning about this was all back in high school during AP European History over a decade ago, so I did have to do a quick search before my comment to make sure I remembered correctly when the transition from the Holy Roman Empire to Austria-Hungary happened as well. I also don't have any illusions that even if my memory of it was perfect, the stuff I learned wasn't necessarily any more accurate than anything anyone was taught to the contrary, since as you mention, trying to pin down an exact date of transition is a bit open to interpretation.
At least from what I remember being taught, Prussia definitely did start to rise in power before the Napoleonic Wars, and the Holy Roman Empire was certainly not a very unified entity (Voltaire's quote always sticks in my mind as well, although I honestly had forgotten who had said it). I think the textbook we used often would talk specifically about the Habsburg dynasty and their sphere of influence in order to be more precise about what was under a more centralized authority versus more independent, and it's arguable that centralized rule over the Holy Roman Empire was already proven infeasible by the Thirty Years War. My impression was that the disintegration of the Holy Roman Empire as a unified entity was more or less inevitable, but where exactly all the pieces would end up was much less clear. Prussia obviously ended up a large winner, but their influence was contested in places; they fought wars against Denmark and France later in the century in addition to Austria-Hungary in the process of unifying a larger German state, and even those claims didn't necessarily last (e.g. France taking back Alsace and Lorraine after WWI). The Napoleonic Wars kind of just eliminated any remaining pretense of Austrian control over the lands that they hadn't really had much authority over for some time beforehand, which made the path Prussia to expand and consolidate easier than ever before.
At least from what I remember being taught, Prussia definitely did start to rise in power before the Napoleonic Wars, and the Holy Roman Empire was certainly not a very unified entity (Voltaire's quote always sticks in my mind as well, although I honestly had forgotten who had said it). I think the textbook we used often would talk specifically about the Habsburg dynasty and their sphere of influence in order to be more precise about what was under a more centralized authority versus more independent, and it's arguable that centralized rule over the Holy Roman Empire was already proven infeasible by the Thirty Years War. My impression was that the disintegration of the Holy Roman Empire as a unified entity was more or less inevitable, but where exactly all the pieces would end up was much less clear. Prussia obviously ended up a large winner, but their influence was contested in places; they fought wars against Denmark and France later in the century in addition to Austria-Hungary in the process of unifying a larger German state, and even those claims didn't necessarily last (e.g. France taking back Alsace and Lorraine after WWI). The Napoleonic Wars kind of just eliminated any remaining pretense of Austrian control over the lands that they hadn't really had much authority over for some time beforehand, which made the path Prussia to expand and consolidate easier than ever before.