History revisionists state that Apple had to buy NeXT as they could not write their own pre-emptive/protected memory OS.
Apple A/UX 3.0 integrated the best of System 7 and Unix. Maybe not the latest Unix available at that time, nor on the fastest hardware; nor with the best driver support. But it rocked for its time.
From memory, Apple needed to created A/UX to permit their hardware to be sold as “POSIX” compliant to US DoD. With more internal, less “not-invented-here” thinking – the need to have a bogus OS (Copland) and the ultimate reverse take-over by NeXT could have been avoided.