Reaction time and PK are different.

It increases mission success, slightly, for the JASSM/JSOW, since they reduce the time they are “fired” at by the S-300, if that even makes a difference, as during the time given against even stealthy targets, an S-300 battery might run out of missiles. That’s a calculation you clearly have not done.

If you don’t have time to react, then you’re going to have a pretty low probability of a kill.