No no no no no, it's not best of 3 in each mod. There are 3 games of each mod, but the result of the match is determined by the total of all of the games combined. It's not mod-specific. Whichever clan gets 8 or more wins in the 15 total games wins the round. If you don't want to use the war system, it's not an absolute requirement, but it is a very good safety net in case of any discrepancies. Whether or not you use it though, the matches are still based on the total number of games, rather than mods.
Also we now have a much cleaner representation of the bracket in place courtesy of Holo. Thanks Holo!