From all Prussian memoirs that I have (and I think I have the bulk of them, cf. www.napoleonzeit.de -> Memoiren und Biografien -> Preußen) it becomes clear, that the wars of liberation were considered by the participants as the liberation from a foreign power which tried to hold their yoke on Prussia and other countries - there is not a single counterexample. For many other German (i.a. non-Prussian) memoir writers - but surely not all - can be said the same.
Regarding the size of Prussia (measured in square miles and population), I am not sure whether the Prussia of 1815 was much larger than that of Prussia in 1805, at least this quantity was negotiated with Russia, Austria, UK etc. in the 1813/14 treaties. Prussia gave up (1814/15) land in the East (from the former Poland) to Russia and won land in the south (parts of Saxony) and in the West (Rhineland), but lost "old" territory in the West (Ostfriesland), too. Ostfriesland was transferred to Hannover. Moreover I think, that a winning power, that had had a major load of a war, will not have after the war less size than before .