Oh boy this is a trip down memory lane. Yes, that was a major part of the mid-2000s zeitgeist. Sure, by that point the two Matrix sequels had largely stifled interest in the Matrix franchise (the previous "edgy" cultural touchstone),... but Harry Potter had plenty of room for edgy stuff (as evidenced by the torrents of fan fics, My Immortal was written and first spread in 2006-2007 just as an example). South Park and Family Guy were seen as rather fresh (IIRC) back then too, etc.
There were several video game edgelords popular within their respective fandoms at the time, partly because that was seen as "mature" by a largely teenage fanbase: Not just Sephiroth and Shadow, but also characters like WarCraft's Illidan (who like Vincent has a demonic transformation). And that was further amplified by sites like NewGrounds, Fanfiction.net and early YouTube in its "Unregistered Hypercam 2" glory (?).
This old Flash-animated battle between Link and Zero to the tune of Linkin Park's "In The End" is in retrospect a prime example.