Servant or Master?

[Nazgûl-king]

While at the end of the Valaquenta in The Silmarillion it says:

In all the deeds of Melkor the Morgoth upon Arda, in his vast works and in the deceits of his cunning, Sauron had a part, and was only less evil than his master in that for long he served another and not himself. But in the after years he rose like a shadow of Morgoth and a ghost of his malice, and walked behind him on the same ruinous path down into the void.

So it seems to me that they are pretty much equal on the scale of being evil, except that for a time Sauron severed Morgoth rather than himself.