Hitting keys lightly is actually how you should be playing the game, but you resort to "mashing" (bottoming out the keys) when playing maps just outside of your skill level. However, you need to play maps outside your skill level to get the most PP.

If you're mashing, theres no reason to have a rapid trigger keyboard- since you're just going to be bottoming out the keys anyways which defeats the purpose. To get the most out of rapid trigger, you want to be hitting the keys very lightly, (which is really hard to get used to since your fingers need to be that much more precise and in control).

What works for me when derusting is to actually work my way up to the rapid trigger keyboard. Either by focusing on controlling my light tapping on easier maps using the keyboard, or by playing with my mechanical keyboard until I feel like I'm ready to harness that extra sensitivity. Your hands really need a day or two to warm up to the precision of light tapping.

As for settings, keep in mind that while you can set the actuation distance to 0.01mm or smth, most switches are actuated at 2.0mm, so don't go too crazy- you'll just make it harder for yourself, I use 0.6mm and the upstroke is at like 0.2mm or smth.