but like a mountain before a storm, Alexandros stood his ground. Words of caution, of anger, words calling him a child, foolish, arrogant, they washed off of him like so many streams tumbling down a mountainside. All that remained was him, and his will, when five minutes later the tumult died, and all saw their words were for nothing.
First, the middle simile "like streams tumbling down a mountainside" is excellent. It recalls for me the idea in "water off a duck's back" but the tone is entirely different--largely driven by the use of "tumbling" and "mountainside" which creates the impression of furious sound.
Second, you almost have a chiasmus of images and sounds, "mountain - storm - stream - mountainside," which could only be improved by inversion to match image of water running down / washing off an unmoving central mountain.