The big problem with the matchmaking system is that there are multiple goals and you can't satisfy them all.
I understand that they want to have more balanced battles so that on average people should be winning half of their battles. However, the issue is that at the end of the day, people look at the leaderboard and expect that whoever is #1 in each division should be the best player in that division.
In the case of Division 1, the GP range is just too great. 4.5M to 5.9M in a single division means that the matchmaking system will really only match up 4.5M GP to 4.5M GP. So if someone dominates this low end GP range, they can be crowned the champion. There is no way that they are better than the 5.9M player.
If you want to crown a champion for a division, then a 4.5M player needs to be matched with a 5.9M player. If you think that is unfair, then you need to add additional divisions such that the top player in a division really is the best player among EVERYONE in that division.
I think you need to get rid of the 8 player brackets for each week of the tourney. At the start of the tourney, you match the highest GP player in a division with the lowest GP player in the division. After the first round, players with identical records will be matched with the highest GP in the division with that record facing the lowest GP in that division with the same record. Do this for 3 rounds each week.
At the start of the next week, you continue matching players with the same record for the entire tournament, highest GP to lowest GP. Continue this through 12 total rounds and the players at the top of the leaderboard are really going to be the best players.
Alternately you rank all players by GP at the start of each week and create a bracket. Then if 2 lower GP players win, they could potentially fight each other instead of another whale account.
Tie breakers should go to the player with the lower GP since they had to beat a harder opponent.