Bach is so monumental a composer that he wrote a dozen pieces and collections any one of which would put him in the first rank. Take for example, the solo suites for violin:
No-one else has come close to writing music this powerful for solo violin. And he did the same for solo cello:
Then there is the keyboard music. Any composer would be famous forever if he had written just one of these. The Goldberg Variations (here is the young Glenn Gould with variations 12 to 19):
The Well-Tempered Clavier (here is Scott Ross with Book 2 on harpsichord--yes, Bach did preludes and fugues in all the keys not once, but twice!):
Then there are the collections demonstrating that Bach was the greatest master of counterpoint. First, the Art of Fugue:
Then the Musical Offering, here, for contrast, in an orchestral arrangement:
I'm not even going to mention the 300 cantatas, which I have written about before. But I will mention the Mass in B minor, which wasn't even performed in its entirely until a century after it was written.
Finally, the piece of music that Mendelssohn chose to perform in his revival of Bach in the early 19th century and a piece of music that has never been excelled, the St. Matthew Passion:
Let me say again, any composer would be placed in the highest rank if he had composed just ONE of these pieces. Let alone all of them.