A lot of good points and information here. There are 2 parts to this picture that are being debated. I feel the consistency of the cars are definitely due to the advancements Greg stated. I can remember when running "dead-on" was huge. Now it seems much more frequent than 10 years ago in the Super categories and Stock/SS. I used to consider myself a decent "bottom bulb" guy but that was when "good" winning packages were 0.030 s. Now they are 0.010 or LESS!! I can't begin to imagine what the setup of the cars are now for those who consistently go in the money.
However, on the reaction time debate, I feel the delay box does help those who do not understand their car's setup intimately. For FULL tree racing, the adjustability of a delay box can help a racer find a staging/launch procedure that helps make them more consistent than they would be otherwise. Granted you still have to release the button, pay attention to temps, burnout, etc., but the box can help you find a method that works for you. I say this from personal experience where I had a friend who was a terrible bottom bulb racer. His car was set up well but he couldn't cut a light when under the gun...never. He got a delay box, learned how to use it, and after 2 races, bingo...he went to at least the semi's every race after that for the year. INSTANT hitter. When I asked him about how the delay box helped, he told me that leaving off the top bulb was so much easier for him than finding his "spot" on the tree. And if he was slower on a particular day, he didn't worry about adding air to his front tires, or trying to stage deeper, he just rolled the numbers of the box and went racing. He didn't win em all, he still had to learn to drive the stripe, but he said it definitely helped. He even figured out that as he got later into rounds he cut slower lights because he realized he staged the car shallower from nervousness. So the box enabled him to start becoming a better leaver/racer whereas he might never have been without it. Also once he started going rounds, he became more confident, and others started to fear him so there was that whole thing going on as well.
I don't know how much the box helps on pro tree racing, but full tree, I think it can help if you don't have the means to science out your staging process. It doesn't make your physical reaction time any more consistent (you are still you), but it can help make your staging/leave process more consistent. It won't make you a great racer like Rampy, Helms, Fletcher, Biondos, DeFranks, Richardsons, etc. but it can make you competitive and maybe that's all you need.