Prior to AZ, some competent people had doubts if self-taught NN could compete at all with a mature chess engine at its strongest setting. You know how that went

Prior to AZ, some competent people had doubts if self-taught NN could compete at all with a mature chess engine at its strongest setting. You know how that went. The improvement rate of subsequent Alpha revisions is incomparable to what software like chess engines shows. Hence, the tendency to evaluate each one as a breakthrough. Personally I believe that "breakthrough" is a non-technical word that's hard to define, but "improvement rate surpassing most optimistic expectations for a given field at a given time" could probably qualify as a criteria.