frumnotyeshivish (and DY if I correctly understand your stated agreement with fny): Why (per earlier comment) do you have a “hard time envisioning a hypothetical scenario” where both the father or the mother would be equally able to care for the child as primary custodian? Are you working on the assumption that the mother should by default be granted custody and/or do you have a “hard time envisioning a hypothetical scenario” where the father may be equally or better capable?
With normal parents where both the father and the mother are capable parents is there any reason you’re assuming, by default, that one is better than the other? Especially if both parents are working and it isn’t a matter where one is home more than the other.