Wait a minuet, this is either a plot hole the size of a small planetoid or something I really didn't get: why is Leon fighting with the rebels again? I understand that he volunteered to become an artificial Valkyrie in doctor Forester's program, and I understand the research data was stolen, but how are those two facts related, and more importantly: why are they related to him suddenly becoming Dirk Gassenarl? Sure, the rebels stole the data, but unless I missed a very important cutscene, this data didn't contain anything on mind control technology. There was no reason for Leon to disappear or for his personality to change. It's not like they put anything in the artificial Valkyries to control them. Julianna went through the exact same process and she didn't become a brainwashed zombie. In his dying breaths Leon talks about being conscious but not control.
From what I gathered, the process that turns you into an Artificial Valkyria either reduces the person's mental abilities to "What's needed for basic functions". Dirk came into being because - at the time - Leon wasn't in control due to ragnite overdose. It's not in the cutscenes, it's in the fluff material you buy from the shops.
Why isn't he in control? This annoys me a lot because if this isn't explained, 80% of the game's plot is basically utter bull. And it was a good game, dammit.
Leon is in a V0 instead of a V2. Note that the V2's are almost completely silent, no matter what happens to them. No screams, battle cries or taunts. The implication of this and Juliana's turn as one is that the process of becoming an artificial Valkyria does awful things to a person. Leon was the prototype. Whatever the latter subjects go through was worse for him.