NeXTStep was never running on any more/less of a microkernel than OS X.
Mach is essentially a microkernel PLUS most of a BSD kernel wrapped around it, all running in ring 0. It's not very microkernely in a true sense. This was done to achieve performant Unix compatibility, which was a major goal of the CMU research project Mach originated as.
NeXTStep used Mach 2.5, where the BSD personality was based on 4.3 BSD. OS X upgraded to Mach 3.0, with the BSD personality derived from FreeBSD. In both cases all of the drivers are running in kernel space -- NeXTStep never had, eg, filesystem drivers running in user-space like you'd expect from a "true" microkernel.
Mach is essentially a microkernel PLUS most of a BSD kernel wrapped around it, all running in ring 0. It's not very microkernely in a true sense. This was done to achieve performant Unix compatibility, which was a major goal of the CMU research project Mach originated as.
NeXTStep used Mach 2.5, where the BSD personality was based on 4.3 BSD. OS X upgraded to Mach 3.0, with the BSD personality derived from FreeBSD. In both cases all of the drivers are running in kernel space -- NeXTStep never had, eg, filesystem drivers running in user-space like you'd expect from a "true" microkernel.