Vergil stabbed Dante with Rebellion to awaken his DT
I never understood this statement. Where is it said that Vergil's intention was unlocking Dante's DT? I'm genuinely asking cause in the actual game, that's not at all what it seems like. Maybe it's said in some other piece of canon media, I don't know.
Given the fact that Vergil makes a mockery of Dante whole game long, stabbing him with his own sword came across more like an act done to add insult to injury (literally) than to bring benefit to Dante. Additionally, he initially just grabs Rebellion and walks away, only turning around to stab Dante as he was showing signs of getting up. If he had really wanted to unlock his DT (for... whatever reason), then he would have done so right away. On top of that, I don't even see why he would even want Dante to unlock his demon form. Didn't seem like he gave a damn one way or the other.
And all that is regardless of whether or not he was actually trying to kill Dante. Somebody made an argument before, in support of the "he stabbed him to unlock his DT" theory, that being his twin, no one knows Dante's biology and how to kill him better than Vergil and so if he really wanted to kill him, he would have done so, therefore stabbing him with Rebellion must have been to unlock his DT. In response to that, as I said before, I think it's more likely and legitimate to think that he did that simply as a way to humiliate Dante in defeat, and even if you believe that he knew that wasn't going to kill him, the fact that he might not have wanted to end his life (which to me, he clearly very much did but whatever) doesn't necessarily mean he wanted to benefit him by actively providing a way for him to unlock his demonic potential. That really sounds like a stretch to me.
any loopholes you might come up with are not going to stand to more questions
Perhaps so but the majority of the specific ones you posed can be easily explained away with a bit of common sense, IMO.
For example, why didn't Dante split into his demon half and human half when Vergil stabbed him? Yamato splits and Rebellion fuses?
One can make the argument that intention plays a pivotal part. On top of that, when Vergil stabbed himself in 5, he did recite some kind of magic formula of some sort beforehand.
Dante's been stabbed a repeated number of times with Rebellion and he never fused with any other weapon in his arcenal, why now?
Same argument as above can be made, about intention. And plus, he never did get stabbed with Rebellion while also carrying Sparda to create DSD (which again, is referred to as the fusion between the two) and tap into Sin DT. It seems to me that you're taking for granted that Rebellion can fuse with any weapon, when the way Dante ponders about the fact that his father gave him Rebellion is a clear hint to Rebellion being only meant to fuse with Sparda, not just any weapon or even Devil Arm.
Now, as a side note, someone could ask, if intention is what triggers these powers, wouldn't that mean that Vergil did indeed intend to unlock Dante's DT when he stabbed him in 3? Well, the game file there kinda denies that, saying simply entering contact with Dante's blood was what made THAT power work, but for the ones that Yamato and Rebellion showed in 5, which were more... drastic, so to speak, that just might have not been enough.
Why only when they get stabbed and never when anything else gets stabbed by them?
An easy argument can be made that being artifacts from Sparda, they're only meant to interact in those ways with Sparda's blood relatives (or even just Dante and Vergil specifically). Similarly to how Force Edge didn't grant Arkham the actual power of Sparda, and was never going to, as Vergil taunted him about.
To me, a far better question would be (and I talk as someone who hasn't read Before the Nightmare, so if the answer is there don't mind me, but even if it is, it still should have been mentioned in the actual game) how did Vergil know Yamato held the splitting power in the first place. And did he always know about it but never used it cause he didn't know precisely what he would be getting into and so was only willing to use it as a last resort? Or did he only find out recently? Who knows. No, seriously, who knows?
