Also completely struggling with this. I got to about the 3rd dan and I couldnt even fight legitly anymore. So I started doing the cheap Angel/Jack combo, and by the time I reached 12-15th dan I can't do anything anymore. I'm currently at vanquisher and cannot get a match in my same rank.
I've won 13 straight against ranks 3-4 higher than me (by quitting about 20 matches) and I'm still not getting equal rank fights or promotions.
Starting to regret this achievement :/ the AI certainly aren't "easy"