Do you actually need the 3 artifacts ( chaos moliri , astral dominae, destiny dominus ) to reach the cosmic forge? The Dark Savant and Bela doesn't have those 3 artifacts and yet they can reach the place for your final confrontation. Anyone knows?

Well realistically, both the Savant and Bela appear after you place all the artifacts down and open up the portal. I think you need the 3 artifacts to open the gateway to the cosmic forge, but once its open anyone could theoretically enter.