Makes perfect sense. If you take a person who's never lifted weights, ask them to say what's heavy weight for them, lets say the bench press. Lets say they say 60 lbs. Now if you take a guy who's worked out 4 x a week for two years. Ask them what they say a heavy bench press is. They would probably say 150lb+. Now lets look at this by holding a club. What holds a club, Muscles. Your fingers have muscles, your forearms have muscles. So ask an amateur who rarely practices, who just goes out and plays what they think they hold the grip as. They might say 8. Ask a pro the same question, who's hit thousands upon thousands of golf balls. They would say 5 or less, hold it like a bird i think Tom Watson said. So, its the same thing. Pros have more strength in their hands. So, when they say, out of 1-10. That means much much more for an amateur.
Also, most amateurs probably don't grip the hell out of the ball. I can tell you i see no one do that in the leagues i play in. Most of them hold the club enough to hold the club. Maybe if they have worn grips, the might grip harder, but they don't death grip it. I rarely see people at the range death grip a club. Most people know that holding a grip tight doesn't feel right. Most amateurs actually grip to soft. Then what they do is, try to regrip during the swing.
I'd just like to add something to this. I work as a mechanic and a maintenance man, so I use hand tools everyday. I'm pretty sure I have a stronger grip than the average office worker. I'm also pretty sure that weightlifters could probably crush my hands like soda cans.
Might want to check your facts.......most amateurs grip the clubs as if they are holding on for dear life.
On a scale of 1-10; a 5 would represent a 50% tighter grip than 0 and a 50% looser grip than a 10.
I have no clue what you are trying to say with this statement;
"Well if you hit a lot of golf balls and might work out, that could be some other amateur's 9"
Sometimes math is hard......