> After having compared CC24 results with results of profiling directly against spectral databases I'm not particularly concerned with the spectral shapes of it
In real-world photography the blue-purple shifts as well as red being too orange or too magentish are being a plague. The wrong rendition of reds touches upon yellows and causes problems in skin rendition too. In my experience it is target design issue as well as CAT issue. As I make my own targets, I can see it. One of the practical way to minimize those shifts without making new targets is profiling based on spectral response. Using spectral transforms to the latest possible stage and recording light spectrum in the scene is also one of the things I always considered better suited for profiles for photography.
Semigloss and gloss targets were appearing at the time when profiling libraries were designed with the premises that the wider is the range of colours the more accurate will be the estimation of red, green, and blue chromaticities. That started full force with CC DC, and it turned out not to work well even in studio, so Gretag made a special reference with glossy patches being removed from reference data and ignored in the device data. The other hypothesis, including patches for a LUT-oriented cube, also proved to be wrong. Another trouble is that the large white patch in the middle caused flare on the surrounding patches, and CC DC died giving place to CC SG. From the point of view of profiling, SG differs from Classic only in reflectance. But Classic also has no patches for accurate flatfielding and flare estimation. In all other aspects classic has advantages over SG even in studio. That is why we included flatfielding in RawDigger, to make Classic more usable. I always maintained that the targets need to be matt, and that in studio Classic is more practical than Passport - given one can mount the Classic geometrically flat.
I think diagnostics of flare and glare and eliminating patches with excessive amounts of those is a good working approach. Indeed, GIGO.
Profiling and linearization are different tasks, solved at different stages. I do not rely on profile LUTs for linearization (one of the reasons is that CMMs introduce too much noise and rounding errors when working with small numbers; and may even cause posterization). As to glare, I have photographic ways of reducing it, as well as object-level sampling and processing data accordingly, so in my own work glare is not an issue when it comes to profiles. In any case, flare in the final scene can't be characterized based on the shot of device-level targets like ColorCheckers being shot for profiling.