Here is the disagreement:
Steve wanted to invest money into Mac OS to integrate Unix foundation.
Board don't see why people would need make Mac OS unix.
NeXT was under contract to not to compete with Apple, so NeXT can only sell to very small number of customers. In addition, NeXT was ahead of its time technically. Result, OS X is delivered 10 years later after Steve was back at Apple.
As I said, Steve owning pixar resulted in the modern apple. I wrote an article on Pixar on my site.
Yes, I remember those Next machines at school, University of Illinois, because Stephen Wolfram, the numerical analysis professor/researcher, had
us doing assignments with his Mathematica application. I chose to use the Next machines (i.e. grey scale or color) because they had a great UI, huge screens, and they were fast. Now, if Jobs was allowed to be creative and realize his vision, then it would have been very possible to see Mac OS X in early 1990s instead of early 2000s. The Next company Jobs founded was successful because it allowed him to be creative and realize his vision without management, board, and anyone else getting in the way.
Speaking of Mac OS X, I have version 10.0 and 10.1 in boxes about 2 meters from me. Also, I have the original manuals for the OS as well as the Objective-C programming language. It's great looking back at personal computer history. Now, if you want to go a little further back into history, Xerox Parc, the inventors of the GUI, ethernet, mouse pointer, laser printer, Smalltalk, and many other things we use today, you can see how history repeats itself because the management at Xerox Parc thought all this stuff didn't have a business future. I guess they couldn't take 43 of the 50 greatest minds (i.e. their employees) seriously.