What they mean is there should be more mid and low (like not everything is really high pitched) it helps give it more... body or like it sounds more full that way
I like this :3 i think the synths could have been changed around a bit. Maybe add a splitter at one of them going to your centroid and one to your rasselbock adding some speed.
i might edit the song at some point I am unsure. I already have a whole album ready i just haven't gotten around to getting it ready to release because im lazy :P