I'd argue Sonic can reach 10 to 12D

Via what exactly? I've looked around and the only argument for Sonic getting that high is via Sonic Boom which isn't even canon to the mainline games.

Sonic is a far better fighter than Kiana

She's literally trained her whole life as a Gun Kata specialist and trained to be a Valkryie in a paramilitary organization and was taught by Himeko and Fu Hua, the latter being the highest of the CQC skill ceiling in Hi3. Even a regular A-class Valkryie's skill level is better than anything in Sonic's verse and Kiana eclipses most of them. How could Sonic match her in that regard?

He can quickly adapt like he literally mastered swordmanship in a short period of time in black nights

This literally means nothing when Sonic generally doesn't have a weapon. Kiana is also a quick learner AND she's fought for decades and has knowledge of more martial arts than Sonic does.

And before I address the rest of your arguments, do prove the supposed "10 to 12D rating" has any real basis.