This achievement takes a little bit of time, but if done correctly isn't that difficult to obtain.
I completed this achievement using a kickboxing/BJJ combo through all five play throughs. The key to making this achievement as easy as possible is to set the difficulty to easy. At this level you can simply bang through most opponents with relatively little trouble.
I would however be careful of the ground specialists (Mir, Maia, etc.) as they can easily submit you even at this level, and add an extra match or two to get the title.
If the current champ happens to be one of these fighters work to increae your ground defense in training and during the match work to get back up to your feet the second they have you on the ground. If you can stay standing even the ground specialists offer little trouble at easy difficulty.
Using this method of picking my fights against non-ground specialists I was able to win each belt in around 8-11 matches depending on the weight class. Total time was around 2 hrs per belt...so about 10 hrs total.
Should you have anything to add or an idea on how this guide could be improved please contact me either in the comments or through the TA mail.