It's interesting to note that even "100%" synthetic lubricants need something like 20% mineral oil "additive packages" before they can be used in a modern automotive engine...
Yes, I don’t 'carrier oil' is a really big issue anymore.
RP supposedly used/uses a fair amount of mineral oil as 'carrier oil.' A couple years ago, they openly referred to their street oils as “synthetic blends” but they haven't described their oils as a blend in at least a year.
With the Group III oils calling themselves “synthetic,” I don’t feel the carrier oil issue is really that important anymore.