Unfortunately, if there were such setting, someone would have found. In previous iterations (FSX/P3D) there were configuration files with light scalars you could edit to get clearer PAPI or runway lights.
IRL not all airports have the same equipment. Large metropolitan airports will have state-of-the-art lighting with variable intensity, while smaller airfields might have very basic systems.
Agree that approach lights have not been done properly. First of all, 24x7 operation is simply not realistic. When an airport has good equipment, at high intensity, the PAPI can be seen for really far away! Approach lights are not omnidirectional of course, the RAIL (twin flashing lights at the runway threshold at the approach edge) in the sim is flashing like mad, rabbit lights are not intense enough in the sim and behave completely differently than real life (the real lights flash extremely fast and once per second or so).
There could be improvements, but I guess that’s not #1 priority for anyone. You can all vote here
or here