« microkernels are easier to port » is not a thing.
NeXT did make their own hardware, it was 680x0-based and it was nicer to use than the x86 PC shitboxes it ran on when they stopped making hardware.
« very little assembly » is closest to the truth. NeXTstep and OpenStep were written almost entirely in C and Objective-C and compiled using the GNU toolchain. NeXT was always a hybrid of Unix userspace on top of a Mach microkernel. It’s just not that hard to port a Unixlike OS to another CPU architecture. It’s literally been done since the 1970’s.
However, it is much more difficult to port the OS and maintain binary compatibility with apps created for the previous CPU architecture, which has always been Apple’s special sauce since the original PowerPC Macs.
The hardware certainly looked nice (I have a "turbo" slab in my collection!), but the performance was "meh" at best. NeXTstep needed a lot of resources, and late 680x0 was no match for an early Pentium. It's no wonder NeXT ported to x86.
« microkernels are easier to port » is not a thing.
NeXT did make their own hardware, it was 680x0-based and it was nicer to use than the x86 PC shitboxes it ran on when they stopped making hardware.
« very little assembly » is closest to the truth. NeXTstep and OpenStep were written almost entirely in C and Objective-C and compiled using the GNU toolchain. NeXT was always a hybrid of Unix userspace on top of a Mach microkernel. It’s just not that hard to port a Unixlike OS to another CPU architecture. It’s literally been done since the 1970’s.
However, it is much more difficult to port the OS and maintain binary compatibility with apps created for the previous CPU architecture, which has always been Apple’s special sauce since the original PowerPC Macs.