I felt the same way about my Gen 3 G23. The finger humps didn't fit my hand, but everything else was perfect. I used a sander to remove the humps and then smoothed it out with sandpaper of increasingly finer grit. Finally I used a soldering iron with a straight slot tip on the frontstrap in X patterns until it finally looked like rough sandpaper. The grip feels like it had a slight grip reduction. I also sanded the part of the trigger guard above where the middle finger rests to allow for a slightly higher grip.
If I wanted to reduce it more, I could heat the hollow area at the bottom of the backstrap and press it in against a flat surface. If you choose to do this, make sure you insert an empty mag before pressing the backstrap so that you don't go too far and the mag doesn't fit.
If you DIY, don't use a dremel tool, and take your time. Its better to take off too little and the job take longer than to take off too much and you can't undo the damage. I started out filing it by hand, then I used a flat sander (very gently), and then took days to finish it with sandpaper.
I wish I had a better picture but my phone's camera isn't very good.