That defence does not stand to scrutiny
AMD is exempt from the mandatory address space separation in the Linux tree as of now. Linus merged the patches.
Based on the way the code stands (when code speaks marketing and PR hack should shut the f*** up), AMD is not vulnerable.
Ryzen looked good prior to that anyway. It now does not just look good, it looks stunning. My guess is that AMD is about to get a serious inventory issue with not being able to print enough of them.