To add on to this, with many European royal families being the behemothic entities that they were, was the "clout" of a nation at all based on the history of the ruling family- i.e. If a new family gained the throne could it "ruin" the reputation of a country's monarchy?

I can't speak to the Brandenbergs, but the Habsburgs are my area of expertise.

The Habsburg rulers, though gaining their power relatively late in the game, were able to utilize a mythos which linked them to the old Roman emperors. In this way, they were able to portray themselves as having a long noble lineage and were accepted as such by the other European powers.

This pedigree was compounded with the specific brand of Austrian piety (Pietas Austriaca) which legitimized their rule through religious means. The founding myth of their new dynasty lay with a very particular story of Rudolph of Habsburg in which he offered his horse to a priest who was carrying the host after supposedly being led to him by the sound of a bell (in this version of the tale, the call of God). Again, this allowed the Habsburgs to base their identity and their legitimacy on their historical pedigree and with a divine sanction.

TL;DR - If anyone saw the Habsburgs as less legitimate than older kingdoms at first, this was quickly squashed through an appeal to history and to God.

Sources:

Coreth, Anna. Pietas Austriaca. Translated by William D. Bowman and Anna Maria Leitgeb. West Lafayette, IN: Purdue University Press, 2004.

Tanner, Mary. The Last Descendant of Aeneas. New Haven: Yale University Press, 1993.

Austria's rise, or more precisely the Habsburgs' rise, did take quite a long time. The HRE succession within the Habsburg family was not nearly as given in the beginning. The Habsburg were able to become HRE emperors due to Sigismund, elector of Brandenburg and reigning emperor, had no surviving children. Albert II of Habsburg was elected king of Germans, ordinarily to lead into election as emperor, but died before he was coronated. His son Frederick III of Habsburg was lucky enough to survive and be coronated emperor. The next in line, Maximilian I, gained the Duchy of Burgundy through marriage to Mary of Burgundy but lost his son Philip the Handsome. He had to put in a lot of political effort and bribes to ensure his grandson Charles V would be elected King of Germans, and eventually Emperor. And that, only after Charles V survived a bidding war against Francis I of France, who put himself into consideration for Emperor. It wasn't until much later that the Habsburgs were able to control election sufficiently that it became certain.

When you mention Brandenberg, I assume you meant "Prussian Brandenburg"? If so, then you may want to know that when Frederick III Hohenzollern of Prussia was able to elevate the Duchy of Prussia, previously a vassal of Poland, into the Kingdom of Prussia, he was styled "The King in Prussia" instead of "The King of Prussia", as there could be no other king within the HRE.

When you consider France in the same era, you should note that France was not nearly the centralized state that it became during the reign of Louis XIV, and continuing to today.