Isn't Alchemy just a reverse S-Curve on the Luma Channel. I've been able to re-produce the exact same effects in Resolve by adjusting the Luma Curve even atop incoming RG4 imagery.
Without Alchemy:
With Alchemy:
RG4 shot in Resolve, with Reverse S-Curve (saturation to taste):
Without Alchemy:
With Alchemy:
RG4 shot in Resolve, with Reverse S-Curve (saturation to taste):