I was born 1960 and would have credited at least This Land is your Land to him. And Where have all the Flowers gone. I didn't know about We Shall Overcome (thought it was an age-old spiritual) and to my eternal shame would have credited Turn, Turn, Turn to Robert Zimmermann. Or Bob Dylan.
I just had him and Woody Guthrie jotted down in my memory banks as the godfathers of American folk music that is not just C&W (nothing wrong with the latter). And if it wasn't for them and the people who followed them like Bob Dylan, Elliott Murphy and James Taylor, all rock music lyrics would still deal with boy meets girl and tutti frutti, so, yes, I think Pete Seeger is a little relevant for what this forum is about too.