I tend to think that anyone who shoots the FAST with regular success under 6 seconds, is probably working on every aspect of their shooting rather than just using the FAST as a drill (rather than a test) to do well on the FAST.
The FAST completed successfully under 6 seconds (in my experience) is primarily a test of manipulations; concealed draw speed and reload speed being primarily the largest determining factors to success with the FAST.
To get there requires a hell of a lot of time drilling those two component aspects of the FAST. I've seen Master class level IPSC shooters who can't get under a 6 second FAST with their competition guns. It's a HARD test to complete under 5 seconds for those who work really, really hard at it. And I really don't know anyone at that level who drills only the FAST enough that it would ingrain bad habits.