That wasn't the case with my 5700. The one I had was very slow to
focus in low light and kinda iffy at it.
I think it is very possible that yours might have needed adjustment
(or been broken). I had two 5700s at one point. I ordered a
replacement for my original one, only to find out that there was
nothing wrong with the original anyway (turned out to be a bad CF
card!).
Anyway, the point is, I was able to compare both 5700s
side-by-side. One had noticeably faster/quicker low light focusing
than the other. Sitting in the same room, pointing at the same
view, one would almost always outperform the other. Both were
"acceptable", in my view. But one was noticeably better. I have a
feeling that Nikon isn't doing the QA it should be doing on these
5700s. Ah... market pressures and all that!
BTW, I ran the hot/stuck pixel tests on both too. One had numerous
hot pixels at speeds as high as 1/60th second, with much more at
slower speeds. The other had NONE all the way down to 2 seconds!
Luckily, the one with the hot pixels was the same one that didn't
focus as good. Guess which one I sent back?
-Frank