The memory bandwidth is a small thing compared to the massive win you get by not having to move data between two memory pools at all.

Often you don't move memory around as a programmer, but that's exactly what happens in the background.

It's the address space that's unified, not always the physical hardware.

The data movement (when needed) is handled transparently in the background by page faults and other tricks.

Depends on your workload. And AMD has supported unified memory long before Apple Silicon existed anyway.