All of the latest security schemes combine something you have (device) with something you know or are (password, PIN, fingerprint, etc.). This works fine for desktops and laptops but as not well for mobile devices that are frequently unlocked in public places where someone can surreptitiously obtain the "something you know" part and then steal the device (which is easy). So for mobile devices something else needs to be done.
Biometrics are good because it avoids the situation where you have to type something in. But they don't always work. The best solution for now is to avoid entering your passcode in public if at all possible. But there are 1.5 billion iPhone users around the world and there is no way that everyone is going to be that diligent about it. So blaming victims of device and passcode theft for not being responsible enough about security is absurd, especially if they have done everything else they could, such as using strong PINs and enabling 2FA.
I've got my phone locked down in every way I can think of but if someone gets my phone and passcode they could still do a lot of damage because I can't completely erect a firewall for my email, iMessage, iCloud, Apple Store, Apple Wallet, etc.
There is no way to prevent someone with the device and passcode from doing harm especially within the first few minutes before the owner can remotely lock the device. I don't know what the best solution is but there's got to be a better way to deal with this situation.