This is a very common complaint, and the main reason is that it’s way more complicated than it sounds. The duress feature is designed to immediately erase any chance to recover the unencrypted data from the phone by destroying part of the data used to derive the decryption keys

Sure, but IIRC that does not help if the attacker can retain the device or clone it, yes? Once they have a copy of the raw data they can just throw a datacenter at it, for any future amount of time.