Just to verify, did you test against the OkishDRT or the ZCAM DRT with the derivative driven desaturation?
Do you find that this behaves similarly to per-channel transform like rgbDT in HDR or is it worse? The default settings I have there push things a bit and I wouldn’t be surprised if HDR would have to have its own settings.
This to me too is still something to explore, to try and still have the ability to hit those corners with this technique. That is one thing I like about the current approach in ZCAM DRT.
Edit:
It occurred to me that the derivative used to do the desaturation is effectively just a mask, so it doesn’t have to be the exact derivative. It can be modified, or based on some other tonescale or be in fact any compatible curve. I tested with Daniele’s original MM tonescale and used its derivative as the path to white (but not as tonescale) and it works fine. The flare parameter can be used to precisely affect the saturation in the shadows, contrast changes the saturation in the mid tones and the peak luminance can be used to change how the top end desaturates. The only thing it can’t be used to adjust is the shape of the shoulder, which would be nice extra adjustment to control the top end saturation more precisely. Having parameters separate from the tone scale parameters probably makes sense.