They didn't try and explain that away, though. It's medicine from the future, it IS magic. If McCoy stopped to explain how it worked, and it violated KNOWN principles about how things work, you'd have a nit worth picking.
Unfortunately, they didn't handwave the power failure away, they explained it. And the explanation is stupid and not conducive to things like, uh, life. Better to say 'magic' than to explain it in such a way that you KNOW it's stupid.
You keep flailing at this, but I'm not sure why you're not getting it, as it's been explained several different ways. We accept transporters and warp drive because it's "future magic". We don't know how it's supposed to work, so can't say they're doing it wrong. When you set things in the here and now, and try to explain it with common concepts, it's easy to poke holes in it, because we UNDERSTAND how it works (and why what they are saying is dumb).
If I explain the Warp Drive in technical terms, you can't tell me I'm wrong, only can identifiy if I'm consistent with what has already been said about it.
If I explain how a normal car works, you can tell me that I'm an idiot when I describe it driving across lakes, flying, and that its headlights cure cancer. And it'll look really stupid if I tell you the seats emit death rays all the time, and next moment I show our characters sitting in those seats with no harm done.
They just picked a stupid explanation, one we can RECOGNIZE as stupid. And you're the only one digging in your heels