15. Stasis Rune
To be honest, if this was a list of the most disappointing items in Breath of the Wild, the Stasis Rune would be on top. For one thing – and not to sound like a curmudgeon – reducing the most basic, Zelda-y items in the game to abstract "runes" just annoys me. On the one hand, it's cool that you have unlimited uses of things like bombs and magnets, but by eliminating the notion of scarcity, doesn't it also rob them of their mystique? Maybe I'm overthinking it. Anyway, Statis specifically disappoints because of its limited functionality: it doesn't freeze the entire world, leaving Link to have his way with it: it only stops time for a single object (or, after you've upgraded it, a single enemy, and more powerful enemies snap back into the timestream almost immediately).
But I guess it is useful for stopping giant boulders from crushing Link's bones to dust, and that's not nothing.