He may well have made the right decision... or he may have just made the decision to use a 'mature unix' foundation, because it was basically just reusing his baby from NeXT (and we all remember how that company was taking the PC world by storm right? =scoffs=)
Jobs personally spearheaded NeXT with a small group of engineers. He knew exactly what he was doing. I remember him talking about NeXTStep and he openly boasted about its portability and high degree of hardware abstraction. He tried to sell this idea to other software companies but no one bit. It is no coincidence that OSX is so portable. It is by design.
You seem to imply that if someone is not a coding ninja, then they have nothing to contribute to software. I strongly disagree with this. Job's strength was that he saw the broad arcs of software design. He realized that simplicity and cleanness was key to good software, to maintainable software, to portable software. He realized that if software was not written properly at its earliest stages, it would remain inherently flawed no matter how much it was maintained.
It is no coincidence that Jobs made his best software when he was working with a small team of engineers. This is how he created NeXT. And this is how he created the original iPhone.
As for your comment on NeXT, well it became OSX, so it was in the end extremely successful. And another little thing came of of NeXT workstations. Tim Berners Lee first implemented hypertext on a NeXT workstation...that was the beginning of the web as we know it today. If you had every used an NeXT workstation (as I did), you would realize that the cleanness and elegance of the OS likely had a lot to do with Tim Berner Lee's invention. There was simply nothing like it at the time.