That may be, but judging by the CXB3070 bins, the 90 CRI may still be less efficient of a spectrum because generally to increase CRi they need more red. Mor red means a further shift away from blue, and therefore less efficient outcome (assuming they both came from the same blue chip). But if Cree reserved the very best blue chips for the 90 CRi, then it could be possible that the 90 could equal the 80.
@draz makes a good point as well, more of the 90 CRI SPD is falling above 700nm, so more of the useful blue light is being converted into non-photosynthetic far red light and decreasing efficiency.
So if we actually got access to the top bins currently listed for CXB3590 3000K, I would suspect that the 90 CRi would have to use higher efficiency blue chips to match the 80 CRi output. But those top bins 90s may never become available and we may see a higher top bin in 80CRi that does actually become available.
Maybe Kingbrite demand will influence Cree as far as which COBs they manufacture and release to the retail outlets. For horticultural CXAs, bigger is better so if they can get us top bin CXB3590s for a competitive price, they will get a nice chunk up the upcoming COB grow lamp mania.