I put him behind George Gershwin, Hank Williams and Stephen Foster.
That is only because you are not aware of the huge number of fantastic songs Dylan has written. Gershwin, Williams, Foster and throw in Cole Porter, Lerner and Lowe, Willie Nelson, Rogers and Hammerstein etc. as well into the comparison.
Those folks each wrote maybe two dozen great songs. Dylan has literally written hundreds. His songs are gems of word play with lyrics that go right to the heart of life. And the sheer variety of themes and tunes constantly amazes me.
Those written 45 yrs ago still bite and slap you in the face. They paint pictures of incredible clarity and reality.