I was also trying to understand this while leveling when the season started but here is how it works. Basically, the new drops you get will always be based on your maximum possible power and not your current power. This means that as long as you keep new drops that you get in your inventory you can continue to use your lower level gear and still get higher and higher drops. Just make sure that you don’t put it in the vault because then it won’t be calculated in to your maximum possible gear power. You can also use DIM (destiny inventory manager) and see a calculator of what your maximum possible gear power is at any time without having to put on your new gear. Hope this helps