I did some comparison between your edit and my new code, to see the differences in sharpness.
Left is my version with radius=1, amount=400, threshold_low=10 and threshold_high=50. The input image is the RT output without sharpening.
Right is your RT version (I have used a build from the current RT dev branch).
My feeling is that your sharpening produces crisper details, on the other hand my version, while slightly softer, has smoother transitions between sharpened and non-sharpened areas.
All-in-all this is only visible when pixel-peeping at 1:1 or more, while already at 1:2 the two versions are practically undistinguishable…