"My headcanon is that the energy exchange only works to cure ZYL is because SW has black energy, yeah; if it were a mundane injury, that wouldn't matter, but it's due to black energy corruption. And they're swapping corruption, aren't they? Instead of ZYL having black energy corruption, now SW has white energy corruption - there's an equivalence there, which to me fits with what the Sundial does."

Yeah, I think so too, this explanation makes the most sense to me. Which means that no one other than Shen Wei could have done it at all even if they wanted to, which kinda puts it in a very different context. (But it's still a good thing that the only person who can do it is also someone who can handle it.)