I always start at the end of the equation and work backwards.
In drag racing, particularly 1/8 mile racing, There are two segments of the race. Launch and finish.
During the launch segment, we leave the line around 4000 rpm, or faster, with a good converter and shift a moment later at something like 5800 rpm. The main part of this is getting the car to spool quickly and reliably so the car is well within the power band when the hammer is dropped. From that point to the shift out of first, tuning is not particularly sensitive as the load on the engine is relatively low after the initial hit on the tires. Timing and A/F are not that crucial. The hardest part is tuning so the launch is nailed.
With a good converter, second and third gears occupy a 500-800 rpm band on a good combo. It's really easy to tune A/F and timing on a narrow band with the main emphasis being acknowledgemen t that the torque converter is applying a variable rate load on the engine which means we tune largely on the bottom end of the gears where the load is and ensure top end has just enough. 1/8 mile tuning is very simple because the engine does not have much time to build excessive heat...particu larly when spraying alky.
1/4 mile racing requires a bit more emphasis on third gear because combustion chamber heat can get away from you if not anticipated.
Contrary to all the discussion about processor speed and such, it's all negated by the short time and rpm band in which we operate. A chip will produce the same times and top speeds as an aftermarket fuel management system. BUT, an experienced tuner can quickly adjust to wide swings in ambient weather conditions and adapt to changing track conditions that affect traction if there is a provision for boost control. 24 out of 25 don't understand the process due to being occasional racers that show up a few times a year. Those guys may well be more consistent on a modern chip.
In the end, the faster you are, the more crucial becomes launch-especially if there is a car in the next lane that you have to beat.