I don't know Steve Goodman's catalog of songs well enough to really know where he stands in that respect, pdq. Nor Shel Silverstein's, for that matter. But I sure love those Shel Silverstein lyrics you posted above. They're wonderful.

As to who is the greatest songwriter of all time...well...that's impossible to say for sure. It would be like trying to draw a single definitive picture of the wind. One can hazard some subjective opinions, that's all, and opinions are based on only partial knowledge.