286 and 386 were NOT comparable to 68k. Much Amiga development was done in 68k assembly which was an absolute joy compared to x86, and mapped almost directly to C. Plus the PC was starved for IRQ lines, and the Amiga environment lives and dies on interrupts. Because PCs lacked the Agnus and Paula chips that made the Amiga so compelling, AmigaOS on the PC would have struggled, especially during the 80s, had it been written. Most likely the developers of the day would have declared the task impossible.

IBM licensed some Amiga technology for OS/2 in the 90s, which is probably about as good a "PC AmigaOS" as we'd ever get (absent recent efforts like AROS).