a more succinct answer came to me (i love your question, being a mozart 'freak').
i looked in einstein's book 'music in the romantic era' and realized that for him, romanticism started with beethoven. he would call mozart a romantic classicist. that is, he put his artistic self into his music, even though it was commissioned and he had to follow certain rules and forms. he ultimately broke all the rules anyway. maybe didn't go as far as haydn and beethoven, but surely would have if he had lived long enough.
he did see 'the leveling of the classes.' and, "mozart lived to see this development without really taking part in it. his piano concertos are still highly elegant for aristocratic society, and even his last three or four great symphonies stand just between the chamber and the concert hall - significantly enough, one of them, that in G minor, renounces trumpet and timpani; it is still chamber-art. "
but, i personally believe that, in his own way, mozart started that 'revolution' in music. remember he was kicked out of his role with the archbishop of salzburg and in effect became 'his own man' at the end in vienna. i suppose that einstein really venerates beethoven much more than mozart because on page 346 he says:
"by a thoroughly logical development, it was the land of the revolution in particular that assigned to music, and above all to the music of beethoven, the role of world-improvement - a moral-political-social role. as the revolution had torn the musician, the composer, the performer, the virtuoso - out of his old connections and set him over against the masses as a free individual...to gauge how much conditions had changed since 1800, one need only imagine how bach, haydn, or mozart would have been received in this new order of things."
einstein is funny because he denies mozart a real role in the revolution in this book, yet he forgets 'the marriage of figaro' was the real start of it all (making fun of the aristocracy right to their face) . mozart had guts to bring so many details of common life into the higher order, and so many aristocratic ideas to suzanna and figaro. they are smarter, and keener figures - and seem to have a better grasp of reality. mozart was well aware of the dire circumstances that surrounded him, and i think he did as much as he possibly could within his means to change them. and, to me, the last piano concerto k595 was written to express himself (simple, not affected by aristocratic stuff anymore, and content that his works had brought about a revolution in his own time from old instruments and sounds to very new sounds).
what einstein seems to say is that mozart didn't alienate himself soon enough. he wouldn't have physically survived if he did that. oh well. einsteins books are well written, and very detailed. he is truly a great musicologist, but favored the romantic era over the classical very much it seems.