I know the chart is bogus... but on the other hand it is old (before Cat 5 was invented and maybe long before that). I don't remember where it came from, but supposedly someone thought it was typical at one time.
Lindsay Blount might be well above 5 W/kg on FTP. I was talking to some other guys in my race around the breakfast table one morning, and they said there was someone in our race with FTP of 5 who was only mid-pack on the Mogollon climb (where his avg was ~4.5).
Boyer, who I think finished 12th in the Tour de France one year, only managed 7th on Mogollon and 5th overall!