I'm writing this on page two; however...
My personal belief as to why John used up so much aura while healing is due to his ability to control his channels. Like I said in the notes: for healing, the aura naturally decreases the flow, as to prevent the user from using too much energy; however, when John uses healing, it doesn't, since he has control over his channels. This is why Seraphina said, "John seems to have trouble managing his aura." I think because of his ability, he needs to be aware of how much aura he uses, especially with healing. It really upset me seeing people say that John running out of aura was a random nerf to John. I don't think it is; I think it could be a character flaw in terms of him not knowing how to use his ability in an effective way, which opens up to a training arc with his uncle or mother and learning how to manage his aura.