Lightweight is clearly a division where the UFC doesn't have all the top fighters.
Posted by Pookie
How well would the UFC do?
If it's a Grand Prix, the UFC would do well, because B.J. Penn would win it.
If it's a UFC-vs-the World card with the matchups you named, I think The World would win, but some of the matchups are one-sided. In a tournament, you would either seed the fighters or set the matchups randomly. In a UFC-vs-the World card, it would make more sense to try to balance the matchups.
Posted by gspfan
Alvarez over Griffin via UD
I think a Decision would favor Griffin. That is, if the fight went to the judges cards, it means the fight went the way Griffin wanted it to, and not the way Alvarez wanted it to. Of 16 fights, Alvarez has only gone to a Decision twice, and one of them is widely considered to be a Fight of the Year candidate.