I imagine that authorities will catch on pretty quickly: "keep your hands up and away from your pockets while we retrieve your device." It would have to happen before any kind of duress.
The tech community's reaction to this stuff seems to boil down to "it does not solve every single problem therefore it is pointless." Which is silly, although to be fair it seems to be the tech community's reaction to a lot of things.
I keep seeing people mention locking the phone before going through customs. This accomplishes nothing. If they ask for your device, you are required to unlock it. If you refuse to unlock, best case scenario means you turn around and go home. Worst case scenario, you are detained as a criminal. If your plan is to fight back and not allow the agents access to your phone, you won't be making it across the border. Bringing the device with you means you must be willing to unlock without causing a fuss. The only way to "win" is to not bring the device.
If its something to do with security then yes, it is pointless. It doesn't matter how secure your door is if your window is open.
Said another way, the chain is only as strong as its weakest link.
How do they know you've disabled Face ID?
LOL. Now the police have the right to physically search random people? The police can do nothing if you put your hand in your pocket and disable the phone.
You are worried about a tiny percentage of cases. Most people are worried about border agents (who have authority as much as 100 miles inland) or cops in traffic stops asking to see their phones. 99% of the time you will be able to hand them the phone and disable it before they get it. They aren't allowed to ask you for the pin-code, so it's game-set-match at that point.
See: stop-and-frisk.