I noticed there was song data errors in places - for example, in this chart (http://www.degeneratestate.org/static/metal_lyrics/clusters....), in the most representative songs for Tiamat, it lists White Pearl, Black Oceans. That is a song by Sonata Arctica. It also lists 3 versions of the same song for Nightwish in most representative songs (Elan). Similar mistakes are made for various bands in that chart (Symphony X, Hammerfall, Therion, Sabaton, Stratovarius, Helloween, Within Temptation, etc.).

This was interesting to read in general though, especially as someone who listens to metal quite frequently (mostly of the power metal variety).