1. Beethoven's music is much better than, and must be rescued from, its posterity.
2. The German/Austrian canon is a late, nationalistic, ideological fabrication with little real background, if at all: with few exceptions, for each and every composer in its top 10 there is at least one non-German/Austrian, or one neglected German/Austrian, of equal musical quality.
I don't understand 1.
I'd like to apply a few distinctions to 2. There are without question a few extremely important and influential composers from Germany/Austria. I disagree that for Bach, Haydn, Mozart, Beethoven, Schubert, Brahms and Wagner there is at least one other composer of similar quality and importance. Maybe Brahms is not quite as important as the others but I think he is still by far the most important non-opera composer of his generation (born between ca. 1820 and 1840). For Bach one could argue Handel (which would be odd because he was German as well) or maybe Rameau. But I don't think many would agree.
EDIT: I might have misunderstood the claim. I do not disagree that for each of the top 10 German/Austrian composers there could be found a roughly equally important composer,
if one can pick from the whole of music history (like Monteverdi, Stravinsky etc). But I think that among their respective contemporaries these guys (Bach, Mozart etc.) dominated (or dominate in the retrospective canon) for good musical reasons and that this is not a mere fabrication by Philipp Spitta or other 19th century music historians.
However, I agree that forming composers from about 200 years (say Bach to Schönberg and Hindemith) into one line of tradition and connecting this with something "German" is problematic or even nonsensical and was probably inspired by 19th century nationalism. Germany and Austria were rather distinct countries and different cultures for most of this time. And, more importantly, the influence and impact of these composers, both as input and output, usually was very "European". It is disingenious to think of Haydn and Mozart or of Brahms, Bruckner and Wagner as "national schools" like one could with some justification in the case of the late 19th century Russians. And I would argue that this is precisely why they were so important. They "transcend" the national schools.
It is somewhat different with opera because this was Italian/French dominated, so unlike in instrumental music there was a conscious effort to establish German language opera. But Mozart, who started German Opera for real (there was German baroque opera but it did not amount to a distinct style, I think) also wrote equally or more important operas and his style was strongly italian-influenced. In any case, nobody would seriously claim that German opera was as "dominant" as instrumental music in the canon/repertoire, so this may be a moot point.
