It isn't. TouchID and Yubikey are in the same security class they are both HSM devices with physical presence tests. A HSM with a fingerprint reader is actually

It isn't. TouchID and Yubikey are in the same security class they are both HSM devices with physical presence tests. A HSM with a fingerprint reader is actually better than a Yubikey as it has a stronger presence verification. The only real advantage of a Yubikey in this case is portability. The parent is comparing to a key living in software, which TouchID is not.