Recreated my scratched chromeball scene again, and:
Fstorm:
A lot better looking bump, much more fine details, only creates bugs when bump is way beyond any normal use case
It does not seem like there's any filtering/blur on textures by default. Turning this up creates similar bump as in Corona, but without disappearing from far away.
Adaptive sampling is very aggressive on the scratches, making them show up almost immediately, but slower at removing the fine noise all over the image
Corona:
Filtering on by default, turning it "off" (0,01) produces much better results, and keeps it looking correct from far away
Not as good bump, trying to match the amount of bump/scratches in FStorm produces a "ring" effect
Adaptive sampling not really focusing on the scratches(?), so it needs a lot more samples, but at the same time the entire image becomes progressively better.
So in short:
Turning "off" filtering on textures is as always a good thing to do, maybe get in the habit of always doing this on bump? Increased rendertimes?
Room for improvement on bump in Corona in general. Take a look at the competition, always good to have something to work towards.
Maybe improve on the Adaptive sampler, it's very handy if it focuses on texture details like the scratches, aka quick feedback when editing materials
PS: Not sure if it's the Adaptive sampler that is deciding what to focus on when rendering, but that is my understanding of the feature.