So that post was a year ago and I don't think I'd necessarily change my main point- that pre-Classical and Romantic music have more in common than Romantic and modern music (defining 'modern' as things like Impressionism, modernism, jazz, serialism etc, not Romantic styles written after 1900). But where I originally argued that in the case of piano repertoire this was down to Liszt's innovations and their influence on 20th c. composers, I now see it as coming from how much the world opened up- meaning composers were now regularly exposed to music from outside of Europe. Only someone who heard gamelan could have written like Debussy and Ravel, likewise Ravel's postwar style would not exist without jazz.
But yes, I wouldn't say "Romantic composers just elevated late Beethoven" anymore. I don't think generic statements are helpful in any discussion. Likewise I wouldn't say Beethoven was always extroverted- eg. the slow movement of Hammerklavier is so powerful because it's a moment of introspection in what is otherwise an extroverted work.
And lastly, I don't believe the piano recital came from introspection. It came from 19th century consumerism- a soloist is less expensive than an orchestra, but you sell the same amount of tickets so there's more profit. This is the seed that grew into celebrity pianists, piano competitions, standard repertoire, and so on.