Learning from experience

Hello Rabbi,
In today's lesson, the Rabbi offered an explanation for the Rashbag's view of the Yevamot that a 3-fold strength is required, not 2 as Rabbi's view, because a common explanation is needed for all cases that is significantly stronger/more likely than the assumption that there is a case here (and not just stronger in some way, as Rabbi's view). The question is how do we explain the Midot Hardash according to Rashbag – why don't we study the Koch or the equal side of three texts, to verify that the parameter is indeed strong? According to Rashbag, is the Midot Hardash a separate category in which a lower level of certainty is sufficient?