I'm not on TPI.
I think, and this is just my own personal thoughts, that accumulated practice may be why one may be able to pick up a pistol and perform at a higher level without having done much shooting for the past year.
I can barely do sub 6 second FAST's now. If I took a year off and then did an hour of dry fire, I would not be able to be even close to 6 seconds. But then, I've really only dedicated myself to learning to shoot two years ago, and really dedicated myself to pistol shooting in the last year or so.
My accumulated practice time and rounds down range is probably hundreds of hours and many thousands of rounds less than you, but many times more than most shooters on this board.
Sub 7 second FAST's are possible without having to spend thousands and thousands of rounds and time at the range. However, I've found that every 10th of second after you break 6 seconds is very hard fought. Consistent Sub 5 second FAST's indicated a rare dedication to shooting and natural talent. That's why I like the FAST so much.
IMO, if you can consistently pull off 5 second FAST's and are not shooting regularly, that is something special.