True, and not just in music. Some people are quick to find villains who killed off schools or styles or philosophies. Sometimes there are such villains and ways of art or life are cut off before they reach their full flowering. But not in this case.
Such things don't last forever. One can't expect that composers would be writing in Mozart's or Haydn's style two centuries later. Eventually their way of writing would have gotten repetitive, predictable, and boring.
That's the way art has worked in the West. It reaches an impasse, and then some new innovation renews it. Maybe this is unfair to non-Western art, but it does appear, roughly speaking, that artists in other parts of the world reached perfection in a style, repeated themselves, and began to decline, without having achieved a true breakthrough to new forms and styles. I'm not sure that this self-renewal in the arts still works now, but it was impressive in its day.
For a long time, Beethoven and romanticism were dominent in concert halls. People who were discontented with that style found their way back to Mozart's classicism or to the Bach and the Baroque -- sometimes played on the original instruments. There's a lot to love in that music. It's more modest and less pretentious than what came afterwards.
But it's not a question of parties or ideological combat. Mozart and Bach were refreshing after years of romantic domination. But if we were living two centuries ago and only heard the classical style, we would probably be completely bowled over by Beethoven's innovation. Beethoven showed what the potential of modern instruments and orchestras could produce, and that was a major revelation.
He definitely "bowled over" his audiences. Certainly the power of his symphonies represented a new phenomenon in secular music since the Messiah is also very powerful. Yet he also wrote things which were almost in the style of Mozart, the First piano concerto for example or Fur Elise.
Beethoven did revolutionize the concept of artist too and the anti-social attitude which grew from his cutting himself off became a caricature. Without Beethoven I see no Byron.