Well, I think I found what triggers the reduction of the heavier "PS4-style" rain effect. I created yet another new save slot and began the game, and sure enough, PS4 level rain density on Batman, the Batmobile, and the environment were present. But here's the problem: once you quit the game and reload the save, the rain effects revert to the weaker version for good. Screenshot proof below...
New save (continuous session, no quit), Same new save (quit and reloaded):
http://screenshotcomparison.com/comparison/132981
As can clearly be seen, not only are the rain effects on the Batmobile diminished, but there is also much less rain falling from the sky and onto the ground. So good news is, whenever this is fixed, you won't have to start a new save, bad news, well, if you want the PS4 level rain effects currently, you must start a new game and never quit.
I wonder what exactly is triggering the reversion after a save is reloaded?
New save (continuous session, no quit), Same new save (quit and reloaded):
http://screenshotcomparison.com/comparison/132981
As can clearly be seen, not only are the rain effects on the Batmobile diminished, but there is also much less rain falling from the sky and onto the ground. So good news is, whenever this is fixed, you won't have to start a new save, bad news, well, if you want the PS4 level rain effects currently, you must start a new game and never quit.
I wonder what exactly is triggering the reversion after a save is reloaded?