I once believed that.
Then I heard the Verdi Requiem.
Live.
When it ended, the entire audience sat, utterly silent, stunned, pinned to their seats, for about 5 seconds then simultaneously erupted into the greatest standing ovation I have ever witnessed.
Now I am not so presumptuous as to label anything the finest piece of music ever written.
But I will admit Beethoven #9 is in the (no order) top five.
There are other “big” pieces ... glorious works (Wagner, Handel, Bach, Mozart, et.al.). But their best doesn’t rise to the level of the Ninth. It stands alone.