It takes too long to rack the slide when time is vital and if you're hurt you may not have two functional hands.
Correct! No time to rack, should be able to fire with either functional hand- which supports a mid-back, leg or chest holster, and an either-hand safety.
Or, there’s the wheel gun back-up.
I can rack the slide on my M9 with one hand as long as I have a solid edge to push the rear sights against.
Like the edge of an open car door for example, or even a table or a chair.
I like having 16 rounds handy, as the first couple of shoots will leave the shooter temporarily night blinded and deaf in a dark environment from the muzzle flash and the loud bang the round makes when the firearm is discharged.
I’ve done a little training in a dark environment, and you can’t see or hear for a a while after firing off a couple of rounds and leaves one a bit disorientated, especially after firing a .357 or .44 Magnum.