I don't see this man as overwhelmed or insignificant in the face of nature. I see this image as depicting man's enjoyment of nature and showing his profound connection with nature. I see this image as a positive statement about man's relationship with nature. The echoing of the tree and arm, for me, is nature's approval of the joy this man is experiencing.
This is one my favorites -- it is so much more than a shot of a man throwing a rock into a waterfall. It tells us just how insignificant man can be in the presence of nature's awesome power. He throws the rock because he wants to taunt nature, but his effort is futile. The wall of water that fills the final layer here laughs in his face. You are right about the echoing rhythms here as well -- the thrust of his arm and pointed finger is mocked behind his back by another creature of nature -- a tree. You caught a moment in time, but you also said volumes about man's prickly relationship with the environment.