this is what the blog post fails to address. Is the FIDO2 hardware key approach abusable? Yes. More so than regular image based CAPTCHA? No, like you said,

this is what the blog post fails to address. Is the FIDO2 hardware key approach abusable? Yes. More so than regular image based CAPTCHA? No, like you said, there are well established services for "mechanical-turking" away the problem.