וכי מאחר שאלו ואלו דברי אלהים חיים מפני מה זכו בית הלל לקבוע הלכה כמותן? מפני שנוחין ועלובין היו ושונין דבריהן ודברי בית שמאי ולא עוד אלא שמקדימין דברי בית שמאי לדבריהן
The Gemara asks: Since both these and those are the words of the living God, why were Beit Hillel privileged to have the halakha established in accordance with their opinion? The reason is that they were agreeable and forbearing, showing restraint when affronted, and when they taught the halakha they would teach both their own statements and the statements of Beit Shammai. Moreover, when they formulated their teachings and cited a dispute, they prioritized the statements of Beit Shammai to their own statements, in deference to Beit Shammai. (Eruvin 13)
If I understand right, Beyt Shammai were better scholars (and as R' Eliezer's case showed, probably knew better), but because B"H were more polite and pleasant Heaven "rewarded" (במה זכו) them with setting the Halachah their way.
Now, the Gemmorah could say simply that B"H were more numerous, but it links their triumph to something completely irrelevant to the truth, IMHO.
Where in our Halachah relying on factors other than intrinsic truth is allowed for setting the Halacha for generations?