ZDoom

Spent some time figuring out the material systems, while PBR does allow for reflection and gloss, the brightness of the diffuse map is less responsive to most lighting it seems, correct me if I'm wrong though. After not getting the brightness I expected, I tried the a/o map as pure white, black, and solid greys, same with the metalness, and roughness maps.

Normal/Spec: The lit color and saturation that comes of the regular spec/normal system is way better than I can get PBR to achieve..

PBR: The gloss is nice which moves around to the source of the light and enhances the normal map (would need to be toned down though, and it wasn't responding to the "glossiness 0-1" setting).

Right now I'm liking the "Normal/Spec" way, anyone know how to get PBR to appear less Dark and less glossy?

I recommend you avoid using PBR textures and stick to normal/specular maps. It is more compatible with Doom's classical ambient light system.

GZDoom's PBR light math lacks the ability to properly take environmental light into account, which is why you're having trouble getting it to behave like you expect. Maybe one day I'll add something to GZD that fixes this, but until then I'd avoid using this feature.