Hey I feel you man. I worked on Ragna's challenges for like 6 hours yesterday and was still unable to get past a few of them. I still can't 22C after 5D, Im not sure why. I recently switched from analog to D-pad (on dual shock) for faster dashes and high jumps, but I'm having a hard time pulling off half circles, and even quarter circles sometimes.
The timing is just so strict on the later combos. Thanks to Kro for mentioning advanced input, I totally forgot about that. Im gonna have to start using it.
I'll just gonna keep brute forcing the challenges until muscle memory takes care of everything hehe. It is frustrating though.
edit: 5d not 6d -.-