The VIDC provided a configurable framebuffer (with choices for resolution and color depth), plus a single "mouse pointer" sprite. Audio was just PCM channels. The Amiga custom hardware did a whole lot more than that.
ARM is not an "off the shelf CPU"? Would you say that the Commodore 64 didn't use an "off the shelf CPU" simply because MOS Technology was owned by Commodore?
Well, yes and no - it is a slightly modified version, the 6510, so in that sense, yes. But in another sense, no, because what did they do, when they found themselves in need of a CPU? They used an existing design. That's pretty much what "off the shelf" means.
The VIC-II would count as custom hardware, I should think, as it sounds as if it was designed specifically for the C64. Same as the Amiga stuff was designed by the Amiga team for use in their computers. And same as the ARM CPU (and the other bits) were designed by Acorn for use in theirs.
