No. Keys are easily (and persistently) added to ssh-agent, at which point it is easy to forward and will generally silently authorize without any further user

No. Keys are easily (and persistently) added to ssh-agent, at which point it is easy to forward and will generally silently authorize without any further user interaction. That reduces it to a single factor. Compare that to a totp challenge or a yubi key plus a password. Having one of them won’t get you the other.