With True Essence powering the Spiritual Artifact, its power indeed increased by more than double!
And this is without him refining it with his True Essence, yet it can still display such power.
If he spends time refining it until his True Essence and the Spiritual Artifact become one.
By then, the power it can exhibit might be several times greater than it is now!
When Qi Refining Realm Cultivators use Spiritual Artifacts, they rely heavily on the artifact's inherent power, finding it hard to combine it with their own strength to produce a synergy greater than the sum of its parts.
However, it's different when a Spiritual Artifact is in the hands of a Foundation Establishment Realm Cultivator.
Only cultivators capable of stimulating their True Essence can fully unlock a Spiritual Artifact's power.
