The problem with math rock is that it has a titanically terrible name, on par with "baggy" or "shoegaze" for Critically Acclaimed Genres With Stupid Names.
The way to describe it: it's not inherently about melody, it's about the idea of patterns and using pacing and structures and rhythms that are uncommon and against the grain of what a rock song is supposed to be. If it was just thought of as "deconstructionist rock", not unlike "post-rock", eventually everyone would figure it out, and fuck 'em if they don't; you can't really say that with "math rock".
