OK - YMMV. Printing the density charts without the corresponsing profile for the media setting produced indistinguishable Lustere & Semi-Maatte results for me - shadow separation at the same (very high) point on the stepwedge. So I used the canned profiles for nearest media types to introduce what seemed like an appropriate difference.
I agree, the linearity is horrible with both of those media settings when used in "ICM - No Color Adjustments" mode, which is why I don't think that's a good setting to use as the starting point for your custom profile. That said measuring the darkest patches with a spectro showed the Luster setting to be slightly worse in my experience. But both are far from optimal IMHO.
Note that when you shift to WCRW, you also change to MK ink.
Says who? When using PK cartridge you can choose any of the media settings listed and still use PK ink. What I found is that the WCRW media setting (used with PK ink) doesn't lay down as much nearly as much ink in the darkets shadow tones as the Luster/Gloss/Semigloss media settings, and as a result you get a much more linear starting point to build your profile from.