score:3
It's not really “calculated”, the visa code does not say anything else than “main destination” without defining it and there is some room for discretion by consulates. Intent matters too (say if you are going to a wedding in France, it could be deemed to be your main destination even if you spend a week in the Netherlands).
Regarding your other question, the first destination is really the first destination. But in practice, I have heard about consulates refusing to consider applications in a similar scenario and deferring to the “first country among equal duration ones”, which has no basis in the regulation.