The issue here I think is not whether we can fix or get the highlights its more about why using legacy is less impacted by filmic and the color preservation mode than if you use color calibration .
I have just tried this with the sigmoid tone mapper as well.
Basically if you set legacy WB to as shot check your result. Now add filmic. By default it will pull in the highlights without the massive artifacts.
Do the same and set WB module at D65 and CC set to as shot. This is not a perfect match for legacy but close. Now add filmic and you get strong blue artifacts. You can mitigate it by changing the norm but still it doesn’t happen with that norm using legacy WB.
Sigmoid shows the same thing to a lesser degree as its default per channel norm must be less like the maxrgb used by filmic. If you change the mode in sigmoid to rgb ratio… I am assuming that means preserve the hue by preserving the rgb ratio you see the same blue artifacts…not the same as you would see with filmic ie not quite as strong but there… But again you only see this using CC module not when you use the legacy WB module… You can also use the global picker in CC and this helps ie not leaving it set to as shot…but this is yet another step required to deal with this…
So this also correlates with advice that AP gave in his video that you could change the norm or let the highlights clip a bit so that you don’t see this…
I think I understand why this happens… and his advice etc but why does this only happen when using CC module and not the legacy WB module…
This is only an n of 1 talking about what happens in this image but I suspect its the same in others…
Someone familiar with the code and CAT might be able to quickly say why this might be???
EDIT…
I checked out your edit…that is quite an array of modules… can you explain the use of the color calibration CAT on top of the legacy WB as shot using XYZ colorspace conversion and then the unbreak profile… it seems like a strategy …just wondering what it achieves??