It's interesting to see written here that the AmigaOS design is not SMP-friendly when I remember several articles written way-back-when which noted that AmigaOS was multi-processor ready. I remember one of the articles was in the context of placement against MacOS.
Was the design and capabilities of AmigaOS over-stated back in the day?
Well I believe statement was that AmigaOS 4 was designed in more SMP friendly manner with some features like new memory managment in oS 4.1 but not before, however I might be wrong.
My experience with SMP is that it enables better multitasking (Windows, Linux) but to be trully used it needs "threaded software" updates, so its not all up to OS. So its long road to go that just starts with OS feature introduced.
Even sharing of one core for OS other for apps, or one managing one running app, is an enhancement to not being aware of other core.