I think getting off of the X is a good idea, when it is practical, but many times there is no where to move due to furniture, seated in a vehicle, unstable footing, etc. A step or two side ways might help, but I have noticed that one thing I noticed in a lot of actual shooting footage taken from surveillance cameras in parking lots, and inside stores, or even police dash cams is that the perpetrators are almost always jumping like jumping beans and can't hit crap, most of the time.
But I have also noticed that someone who stands and shoots from a stable platform often connects with their shots, more constantly.
Shooting and hitting while moving demands practice, and shooting and hitting moving targets demands practice. Shooting and hitting moving targets while moving yourself demands more practice. But I would also say that one basic rule of gun-fighting is don't get shot, which might mean needing to move off of the X. However, shooting and hitting the perp (stopping the threat) as quickly as possible, obviously helps to end the conflict quickly where just moving off of the X doesn't guarantee an end to the conflict.
I would say each gun-fight would have to be evaluated on an individual basis for sure, but things seem to happen so quickly, most of the time, that whatever is done must happen in first couple of seconds, to get ahead of the perpetrator's reaction time, and quick action beats reaction.