They don't do the same thing. All the flaws in passwords can be avoided, the semi-public state of biometrics cannot.
Authenticating access, if you follow standard security practice, should be at least two of, and preferably all three of: something you know, something you have, something you are. Not one or more.
There is no axiom that the flaws of biometrics cannot be avoided. “Something you know” is in fact a biometric property of the brain that can easily be transferred.
Touch ID combines something you have with something you are. It’s easily better for 99.9% of the threats out there that result from weak passwords shares across sites and users trained to type them into anything that resembles the real logon page.
