In discussing the source that Megillat Esther may be read on the 11th, 12th, or 13th of Adar in addition to the 14th and 15th of Adar, the Talmud (Megillah 2a) has the following exchange:
What we mean [by our question] is this: Let us see now. All these dates were laid down by the Men of the Great Assembly. For if you should [deny this and affirm] that the Men of the Great Assembly laid down only the fourteenth and fifteenth, [is it possible that] the [later] Rabbis should have come and annulled a regulation made by the Men of the Great Assembly, seeing that we have learnt, ‘One Beth din cannot annul the ordinances of another unless it is superior to it in number and in wisdom’? Obviously, therefore, all these days must have been laid down by the Men of the Great Assembly, [and we ask therefore], where are they hinted [in the Scripture]?
The Talmud argues that all the dates must have been ordained by the Men of the Great Assembly, because a later court would not have been able to change the law laid down by them. However, in this very paragraph the Talmud cites an exception wherein a later court can overrule an earlier court – namely where the later court is greater in both wisdom and number. Why, then, does the Talmud here assume that a later court couldn't have changed the rules of when Megillat Esther can be read? Perhaps the later court was indeed greater than the Men of the Great Assembly in both wisdom and number?
Is it for some unstated reason taken for granted that no later court could have surpassed the Men of the Great Assembly? Do any commentators suggest this, or offer any other explanation?