Could be…or not. Or is it the chicken or egg question?
Back in the 1980-90’s when “brilliance” started to be introduced into judging is the time when WB’s started to take prominence in dressage. WB breeders are predominantly in Europe. The FEI is based in Europe (Switzerland), so perhaps…just perhaps…the breeders lobbied for judging criteria to give advantage to their larger, heavier (relative to TB’s…think Granat, Gifted), big moving horses and advantage their type of horse…just sayin’…perhaps.
IMHO “back in the day” there was no formal “standard” for judges to judge…as is now done in the L-Judges Training. You could be grandfathered in as a judge based on your riding accomplishments. IIRC judge accreditation was rather informal back in the 1970’s (I was there) so the fact that there were few/no rides in the 80% could be that, as shown by this thread, dressage people are hyper critical and the judges were content to give marks of 8-Good and 7-Fairly Good as their high marks…just perhaps.