Most likely it's related to the IBL sampling which can have a fairly significant impact on perceived roughness without actually breaking the maths - in theory it can interfere with the amount and diffusion of the light coming from the sky It's something that can be worked around but I suspect that supporting panorama…
Yes - calibrated means they come with numbers you can use to set them up correctly in your renderer (assuming you have the control to do so) These are calibrated (or at least i'm reliably informed they are) https://polyhaven.com/hdris I don't think you can just drop the files into painter and they'll magically work -…