> there is no suggestions for how to secure and harden devices without refining these trusted computing techniques. We need to harden these devices.
Because the thing you are asking for is not possible. You have a bad premise:
> And I just don't understand how anyone can maintain that farce when the last year has shown that it's a genuine challenge even for the US FBI to unlock a mobile device without the owners say-so and it's getting harder all the time.
Which has two flaws. First, it wasn't a challenge for them, they were just using it as an excuse to whine about the second one that actually is. And second, the only real security is math (encryption), but it doesn't require any special support from the hardware.
If you have full disk encryption with a strong passphrase and the device is currently locked (i.e. the key is not in memory), the only way to get that data is to have the passphrase or break the encryption, and breaking the encryption is not expected to be possible.
The problem is, if someone has physical access to your device and can compromise your firmware, they can record your passphrase the next time you unlock the device, and then they don't need to break the encryption.
But this is not a thing you can do anything about. If someone has physical access to your device they can just steal it and leave you with one that looks the same up to the point of you entering your passphrase and then transmits it to the attacker. Nothing about the original device can fix that because it isn't the original device.
Similarly they can install a surveillance device in your room that can record you entering your passphrase and then come back tomorrow to take your device.
The only answer to these attacks is physical security. Secure boot does nothing.