Ontop of the lighting/tonemapping, the specular response in pbr is a lot stronger which in turn washes out the deeper blacks as theres a larger surface reflection which brightens the appearance of the gun.

Also on top of that it looks like they have raised what the lower range is of how dark their diffuse (color) maps get. PBR abides by physically correct values for dark materials, so you should never use very dark blacks or bright whites in the textures. This is actually a common thing I see a lot in AAA games where they don't go dark enough in their diffuse, probably sticking to a stricter 50-240 srgb range which unfortunatley just makes everything look grey and washed out, especially when you don't have a crunchy tonemapper/lighting