The inspiration for Weston was modern art, not other photographers. Ditto for Strand. Ditto for Stieglitz, whose gallery showed the latest art from Europe pre-1910. Also Lewis Hine for Strand.
There were individuals who encouraged these men to look at this art, but those individuals were not the inspiration themselves.
After a beginning period in photography my own work was mostly influenced, and continues to be influenced, by twentieth century classical music, from certain books, and from certain painters. And of course, one brings ones own life experiences into the mix.
Those who are only influenced by other photographers without a broader background in the arts end up with not enough of a mix and that is the work that is usually classed as derivitave.
Too often, photographers spend too much time on the mechanics of the medium and not enough expanding their horizons by adventuring into the arts that are unknown to them--not as makers, but as audience.