That might even be why he hates Luke, because he blames him for having “corrupted” Vader to the light side. Hence the whole “I’ll finish what you started.”

Also his obsession with Vader/Anakin relics might have to do with Force imprints. Maybe he wants to get as much out of them as possible, regardless of what eventually happened to Vader. If the imprints can be used somehow, then Anakin’s lightsaber should be really valuable as it was present when he turned from the light to the dark side.