> if Beethoven's music had been lost or misplaced, would we immediately recognize it as "genius" if someone made a first recording in 2018
I'm not qualified to comment on the genius of any composer, but knowing my background, I would say he would have become immensely popular. Growing up, people around me knew nothing about western classical music, not even enough to name a few famous composers. I found cassette tapes in Bangalore's music shops and tried them out randomly. Beethoven quickly became one of my favorites and the factors could not have been either that I was over-exposed to his music through general culture while growing up or that his name was famous around here, biasing me in his favour.
I like to think of good composers as one of two kinds: (1) those who impress novices to the tradition of this kind of music (western classical, in this case) and (2) those who impress long-term aficionados. Based on my own tastes, examples of the first kind would be Beethoven, Tchaikovsky, Chopin, Mozart, etc. and examples of the second kind would be Bach, Mahler, Schoenberg, etc. Of course, these categories are fuzzy, and I'm sure there are composers who would qualify for both categories. However, I think a valid approach to answering your question would be to survey what sort of an impression a composer makes on novices to the genre.
Thank you for making recordings of Reicha's works! I'm not a novice to the genre anymore, but it's nice to have new compositions from the classical period to listen to.