Late for the party and we all know how underwhelming Deathwing was but I'd like to think of this as the boss theme for those who cross the Dark Angels chapter.
Personally, I thought it would have been a better theme for The Crimson Fists, since they apparently have a Hispanic theme to them and heroic last stands against massive numbers and impossible odds are their thing, for which some epic gun-slinging showdown music would be perfect