This seems like an unnecessary adjustment to fudge a flawed scoring system, really. The last match should not be arbitrarily double weighted.

I don't really think it's arbitrary - it's that the final match uses the same system as the rest, so you need to predict both Cloud's percentage and Link's percentage. It's just that in the final match, unlike the other matches, one prediction implies the other. BUT, they still don't have to add up to 100%...

There should be a requirement to add up to 100%, its pretty stupid otherwise.

The reason it's not a requirement is that I don't want to have to add up everyone's predictions to make sure they total 100, and I don't want to disqualify someone if they make a stupid typo. You can't gain any advantage by making them not add up to 100%, so it's just easier to not make that a requirement.
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....TCELES B HSUP