People say things like this a lot, and I don't understand it. Maybe it's because I started training young, but those "half a second responses" and "2 inch error" aren't things that have ever concerned me. When I'm in the moment, I throw a punch when I plan to throw it, and it generally works. If I throw a punch to an area, I'm going to hit that area, and if I'm not confident that I can, I make a "half second decision" to hit somewhere easier/larger. And I will do so with a proper fist, the same one I have thrown thousands of times in the past. The issues won't come from the timing or accuracy needed, or an issue with how I form a fist, the issues will come from my opponent doing something unexpected, resulting in a different body part/limb in the area I'm expecting to hit. The real issue is variability, not timing or accuracy.
Then again, maybe I just am lucky enough to avoid those two issues because of how early I started training, but I don't think that's the case.
