I am certainly no grip expert. I have a difference from right to left also. I try and train my hands together as much as possible. So I like what you are doing with the FG DL and I would do two hand pinch instead of 1 hand. Grippers are surprisingly technical. Do you have the same muscle mass on your thumb pad right to left? Can you get the same set right to left. I guess on grippers I am saying do you feel like you are as technically good on both sides.
I wouldn't worry too much about the difference and just keep training both of them to get better.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin