Class specialization among "Light Bearers" was created by The Vanguard. (Its probably why Lord Saladin is the only Titan to wear a cloak). If I had to guess, I probably would say that Gunslingers (Solar) were first. Followed by Arc Hunters....then followed up by Void Hunters. Part of the problem is that Lightbearers work with The Light in different ways, and seem to have different levels of corruptability. Warlocks work with the Light most directly...and seem to be the most difficult to corrupt. Toland The Shattered is the only Warlock (that I'm aware of) who seems to have given himself over to The Darkness and Hive Sword Logic...and its clear that Toland's moral compass (if not his sanity) is quite broken. Titans are in the middle. They don't work with the Light as directly as Warlocks do...but their allegiance to The City and wish to be protectors seems to keep most of them on the right-side of the street. Although Dredgen Yor was originally a Titan, it was only through corrupting his wish to protect, and preying upon his fear of being unable to do this that eventually broke him. Hunters, OTOH, are individualists. They see the Light as mainly a tool to be worked with to solve practical problems. So they seem to be the most easily corruptible/least tightly bound to the Light. Eris Morn was a Hunter when she went on that ill-fated first raid to destroy Crota....probably through a combination of Ahamkara magic and Hive sorcery....she emerged from the Hellmouth with more in common with a Hive Wizard than a Vanguard Hunter. TLDR: Void Hunters are the rarest of Hunters....and those who do tap into the power struggle to control it and maintain their way. The Void is very close to the Darkness. So while Warlocks can touch the Void and generally reamin with The Light, Hunters find it more difficult.