Only one of my five children shares a trait in common with one of my brothers – his love of chazzonus. A brother and sister can be very different types of people. If they are both raised with yoshrus in a loving home, the fact that the boy is not a “learner” at age 19 does not mean the sister’s children will be that way unless SHE raises them that way. I think Chazal should have looked more closely at the GIRL, who will do most if not all of the child-rearing, and be concerned with HER hashkafa towards support of learning, both her future husband’s and her children’s.
We should consider ALL members of a family and how they interact with one another, in assessing a potential shidduch – not just look at the brothers.