I believe that Tolkien's intention in the sentence is already exposed in everything you have already said.
The Silmarils ended up as instruments of power and desire, because of the Dark Lord. I mean before Eärendil's use of it. And the rings began the same way, as instruments of power, perhaps at first with good intentions on the part of Celebrimbor, but ultimately because of the Dark Lord, the other.
Greetings
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