Pretty much so, yes, at least those pieces written for a particular function.
I would go further and include
all works written for patrons holding positions of inherited or elected power. After all, the principle reason for maintaining musicians at Court (or at noble households etc) was not (usually) for the pleasure their compositions or performances gave, but as a manifestation of the power, wealth, and alleged artistic discrimination of the patron in question... a "publicly acceptable" proof of political power. Visitors, for example, to Esterhazy would come away with a greatly enhanced opinion of His Excellency having seen and heard music-making that excelled that of many of the Crowned Heads of Europe. One could possibly make a case for excluding music commissioned by connoisseur-patrons (such as the flute-playing Frederick II) but even then perhaps his performances could be classed as merely the fullest realisation of the "gloved fist"... the omnipotent ruler who also - did y'know? - also played the flute.
"Soft power" it's called these days. Rather like Condoleeza Rice giving Brahms recitals >:(
If music composed to express opposition to a particular political viewpoint is "political", then it's an obvious extrapolation that music that endorsed that same political viewpoint also has a political content to it, albeit an apparently "latent" one. An easy "test-case" for this line of logic would be the composers who found it "convenient" to support the Third Reich, or at least to cooperate with the Reich for the sake of an easy life and professional advancement. Clearly it wouldn't be true to say that it was only the Reich's opponents (Hindemith, Weill, Ullmann, Eisler etc) who wrote politicised music - the Reich's allies (R Strauss, Orff etc) were just as politicised. And before anyone thrusts my geographic location up my nose ;) clearly the same would apply both to composers who clashed with the USSR authorities and those who reached accommodations with them.. both are politicised to an equal extent - it's unavoidable.
I am still interested to explore how abstract textless music can express "political" ideas, however? Other than by the extraordinarily heavy-handed means of quoting pre-existing music that has an established political leaning? For example Puccini is sometimes accused of anti-Americanism in MADAM BUTTERFLY (viz the introduction to Pinkerton's Act I aria that quotes the American National Anthem)... but how many people notice the Japanese National Anthem (of the time - Japan has a new one these days) quoted during the tea-ceremony showdown with Sharpless, when Cio-Cio-San rubbishes her own country's marriage laws? Surely such clumsy requoting can't be the only way of expressing a political idea without text? Can it?
