im listening to tyler the creator right now and thinking "holy shit, this reminds me a lot of old slipknot albums". in both genres, flow is important. the only huge difference is that in rap music, words>music
and in metal it goes music>vocals. and metal doesnt always rhyme.
my point being, if you took something like ofwgkta or old slim shady and got a vocalist from a metal band to scream it, it would fit pretty well.
the way i think of it is that if it were on a graph comparing all genres of music, it might look like the political spectrum where left wing and right wing are actually not far off, and the graph is kind of in a circular shape.
obviously they're still very different, i'm just talking about parts like this
@ 3:13
and the part in this song at 1:33 is heavy enough to be mixed into a metal song
but then again, this in ns where everybody is super hood and knows everything, so i'm probably wrong. just my opinion that certain parts of rap are very similar to certain parts of metal