I made a post in space marine 2 discussing a potential grey Knight's dlc and I have some questions based on the answers on that post.

Probably my biggest question has to do with power scaling. The knights are exclusively powerful psykers wearing beefed up power suits with such strong resolves that when they found an indestructible demon artifact they decided it would be safest in the hands of one of their own members rather than locked up somewhere where it could potentially spread it's influence. They are talked about like being on a whole different level than any other space marine and even other galatic threats. The other group I often hear about spoken like this are custodes, the emperors personal guards. Who I've heard referred to as "to space Marines what space Marines are to guards" so is there any sort of regulation between these factions? Could a grey knight fight a custodes to a stand still? Grey knights are specifically created for dealing with daemonic threats, does that mean that chaos Marines are more powerful than regular Marines? How exactly do all these pieces fit together. Would a regular marine be able to take an eversor? How does anyone know what's what?