I think convenience is important in this comparison because that generates a context in which TouchID is actually more secure, because it's more likely to be used than remembering and typing a passcode/phrase. Apple have shown the usage stats. There is also the inconvenience for attackers of reproducing a fingerprint through an elaborate process, which again makes TouchID more secure (in my opinion) in practice than a password/phrase.
While theoretically less secure, I would say TouchID in practice is more secure for average users. But in the case where there is the motivation I would agree with you.
Right, and I don't think the author necessarily disagrees with the idea of including TouchID in Apple products as an alternative to 'completely unlocked'.
As the author indicates, "This isn't a knock on Apple, as Thinkpad have embedded fingerprint readers for nearly a decade. My intention is to help stop and think about the place of biometrics in security."
The danger is viewing biometrics as a secure alternative to passwords; it's not. But comparatively few people are technically inclined enough to realize that; with Apple embracing it for convenience, we run the risk of people not understanding the security implications; the author saw evidence of that when asked to implement biometrics for file encryption, which is a terrible idea.
I think I remember the issues: good passwords are arbitrary, hard to guess, can be changed at any time, are used for one purpose only. Biometrics (fingerprints) are none of these things.
While theoretically less secure, I would say TouchID in practice is more secure for average users. But in the case where there is the motivation I would agree with you.