Here's a few things a basic and barebones PC without connections to the outside world
genuinely cannot do that an Amiga can:
1. Measure time with a greater accuracy than 55 ms. Amigas have CIAs which provide microsecond accuracy.
2. Generate raster interrupts the way the Copper can.
3. Display an image based on bitplanes. (Then again, the Amiga cannot really display a chunky image without employing advanced Copper trickery, and then at great loss of resolution. The entire concept is alien to the Amiga hardware, is what I'm saying.) This made the Amiga perfect for sideways 2D scrollers, but absolutely
not perfect for 3D games.
4. Attach 9-pins joysticks and mice with ease. (You always had to use a 15-pins port.)
5. PCs do not have standard hardware support for light pens and potmeters. Then again, who uses a light pen nowadays? (I had
this one for my Schneider CPC464---very nifty and cool toy.)
6. Nor do they have standard support for analog TV out signals (it depends on your video card) or genlocking (which is now handled in a different way).
Not particularly Earth-shattering, but still: unique abilities!