I don't know about the details of the OP's paper, but I'm not sure "difficulty" is the right word... Mathematical rigor is needed in many domains. In my field,

I don't know about the details of the OP's paper, but I'm not sure "difficulty" is the right word... Mathematical rigor is needed in many domains. In my field, "not enough math" could well signify that the description of the experimental results is sloppy, or that you can't check whether the results presented are sound.