The above is a good way to try to represent realism in the game, but I don't think it's important for the gameplay. It's more complicated than it's worth, and in the end if you actually go to all of the effort to design the system, modders using it must spend extra effort designing and testing every single new firearm, and players need to spend more time learning to understand the more complicated system, all just to represent the way that in real life, the time it takes to make an aimed shot scales less than the speed of the person but more than zero.
I think it's also missing that a person's athletic speed may not be very strongly connected to the speed at which they make fine adjustments.
In the end, what little variances you have between real life variation and in-game variation easily fall into the trough of myriad variations in all the other minutiae such as how aimed shot time is affected by lung capacity or even the type of boots the soldier is wearing. I say it's neither worth pursuing for realism nor for gameplay. Instead, keeping small variations in time units between soldiers (realistic) reduces the discrepancy anyway.