Face ID isn’t superior to Touch ID in every respect, and vice versa. For instance, even five years on since the introduction of the TrueDepth camera system with iPhone X, Apple recommends that identical twins only use passcode authentication to unlock because Face ID will not be able to reliably tell them apart. Touch ID did not have this problem. Buying with Apple Pay is also nicer with Touch ID, compared to the double-click dance that Face ID requires. On balance, if pressed to choose just one approach, I think Face ID is the obvious choice though because the best benefits are really great; first time setup is far more streamlined than the fingerprint registration process and the most frequent use case of unlocking your phone is so much more elegant with Face ID. It also has a magical quality that Touch ID lacks. It is much cooler to look at the screen than to place your thumb on a fingerprint reader.
This is what Apple went with since 2017: FaceID only in the name of simplicity and (partly) cost savings. Pre-pandemic, I think they could have gotten away with that strategy forever. Post-2020, the see-saw of tradeoffs suddenly weigh down very much in the other direction. Until the release of iOS 15.4 beta, the return of Touch ID seemed inevitable to me.
The existence of the Unlock with Mask feature probably means that Apple doesn’t have to ship an iPhone with Touch ID again. I would certainly take it as a signal that a Touch ID iPhone is not coming back anytime soon. But I still think they should do it. Long-term, the best iPhone is surely one that offers both Face ID and Touch ID (either via under-display scanner or iPad-esque side button sensor). Users would be bale to set up both types of biometrics, and the iPhone would simply unlock as soon as either is presented it. It really would be a best-of-both-worlds scenario with each biometric’s advantages making up for the drawbacks of the other.
I also think it is somewhat telling that Apple goes out of way to call out the accuracy of Face ID is lessened when using the mask unlock mode, right there in the settings UI. The peak of COVID and mask-wearing is (hopefully) behind us, but it isn’t going away altogether. The Unlock with Mask feature is going to be widely used for years to come, and it doesn’t feel very sustainable for Apple’s solution to this problem to be something that they openly warn significantly impacts the security of your device. You also have the ongoing threat of other wearable items — like sunglasses or even Apple’s own forthcoming headset product — that may impact the usefulness of Face ID, over the course of this decade. Bringing back Touch ID in some form is a hedge against all of those potential risks, and one that many people would applaud.