Having been around +18 handicap for a while, I have been always curious at what things made the biggest difference in handicap. For example, the ideas of separation value make a lot of sense, and I have been putting a lot of time practicing the approach shots and driver at home during the lockdown. It will be nice to put the driver in play after not using it for the last 3 years!! Hopefully that will pay off when the courses open here.
I know it is hard to compare someone who drops a +20 to +18, to someone who drops +3 to +1. So perhaps absolute value in drop is less important than the % drop.
So what made the biggest difference in your game? it could be that fancy new piece of training equipment, or that drill you kept practicing off the course, or that new putter you put into play ...
If I was to look back over the last 5 years, the biggest thing that made a difference for me was just practicing a 7i hitting around 150yds or so --- the one year I did that at the range regularly, my scores dropped dramatically. In fact, I played a couple of rounds using just the 7i and managed to break 90. However, I have not been able to find that form again given the typical reset that happens over the winter here.