Indeed, the gloss differences of the actual Precision Colors PRO9500 inkset are very acceptable, I print on glossy paper with pleasure now.
The OEM's are not perfect either.
Without gloss optimiser this must be the maximum achievable.
The strangest thing is that even with the old inks I could never see any gloss differential or bronzing on Kodak Metallic paper & it's super glossy yet It had quite a bit on Canon Luster paper. The new inks are really good now on the Luster.