Is there any OS feature which is better in AmigaOS than in Linux or Unix?
I would nominate datatypes. The unix side lacks the whip swinger to introduce it at the higher ends of the display stack and make it standard - anything visual is contributed by so many parties. And don't forget all the other files types it handles which can be taken care of by non-display parts.
This is a whole-OS interface and your average unixen typically only extends to the kernel and possibly the display render/compose. You could expect Apple to be able to introduce an equivalent.