"First rank" is the phrase from OP's link, not "first-rate", but in both cases it is not obvious to me that it is wrong for there to be mathematicians with that descriptor in every age. They sound like relative adjectives; "first rank" undoubtedly so, "first-rate" to a lesser extent.
"Who are the first-rate/first rank musicians of $YEAR" does not seem to me like it could be answered with "there were none in that year".