Maybe I'm missing something here but your two points seem contradictory to me. It seems to me that a gun that fits well would tend to index better and reduce the time to first shot accordingly. While fit isn't a replacement for practice and one can practice enough to overcome minor issues of fit, it seems like starting with a good fit can only put you ahead of the game. With a gun that fits well you already start out more familiar since you're not adjusting to the gun.It can make some minor differences, particularly in recoil control. The sort of differences that are measurable and can make differences in competition shoots but are meaningless in defensive shootings. It's fairly easy to shoot faster then you can make decisions, and once you are at that point what's a .0X difference in split times gaining you?
Familiarity matters more, particularly in time to first shot and a good index with a presentation.