re: Percentage of legit strong guys in your gym

You simply aren't getting the time under tension with what you are talking about. If you really want to up the grip strength (Endurance would be my ideal word here), you need to work on volume of gripping exercises. If you can hold the weight with 1 rep, you already proved you have the strength to do it but you did not maintain that strength through subsequent reps. This will conclude that you need to work on endurance.

Sure, you could get stronger on your grip if you continue using it the way you are talking about but you are not making it optimum for advancement.