> Judaism IS based on mesorah.
It is, and sometimes we do not have mesorah and we need to figure it out and create a new mesorah. This is either because information was lost (we discussed this before – Maharal about Bavli method of reconstructing missed information) and sometimes we have new circumstances (Churban, Modernity) and we can apply those Bavli methods (that include sevorah) to new circumstances.
Corollary: when we see people who are not good at applying sevorah to simple rational life problems, these people can not be counted among those who mastered Bavli.