I think the solution was over-constrained. Simultaneously killing 36 death eaters, disarming (hah) Voldemort, and then stunning him wasn't just A way out of the predicament without dying immediately, it's arguably the BEST way. All the limitations Voldemort put on Harry were irrelevant, and all the relevant ones that could've happened, like taking away his wand or shooting him in the kneecaps before he talks weren't taken. Voldemort forces Harry to use his ONE ability he can use without moving his wand, which also happens to be the one that can nearly effortlessly kill dozens of people in an instant? I guess when you look at it has him falling to the power he knew not it kind of works.