If viewed with a more rigorous attitude, Simon actually possesses two treasures.
One is that treasure index finger capable of manipulating mechanical constructs, even transforming parts of flesh into machinery.
The other is the Hand of Precision completely taken as his right forearm, which Alka initially acquired from the Holy Machine Church as a Holy Artifact.
Only through the Church's rituals can it be transformed into a treasure usable solely by its members.
Though it's unclear what kind of exchange Simon had with the Church, at least since arriving at Gemini Island, the Hand of Precision remains under Simon's control.
The Church has not reclaimed it, evidently consenting for Simon to use this Holy Artifact.
Overall, even after being upgraded into a treasure, this Holy Artifact doesn't significantly enhance Simon.
The Holy Artifact essentially serves as an auxiliary treasure, not a complete treasure.
