It would be difficult to compare Bach to any other composer but I think that there are other masters of solo instrumental works. Francois Couperin and Domenico Scarlatti are two examples from the Baroque period. And French composer Charles Koechlin is another master from the 20th century, please listen to his "Les Chants du Nectaire" for solo flute, recently recorded in 1997 by Pierre-Yves Artaud (Sisyphe 001, 3 CD's) Baris Kilicbay