They are hardly forgotten considering the OS was a key influence of Mac OS X and you can see clear features of it today. It was hugely important in the mid 90's graphics and 3d animation era too. Such a fabulous piece of design, both software and hardware. I would much have prefered a world where Next and Mac OS never combined and we had both, as the Mac O7-9 were also a real treat to use.
NeXT would have died and Mac OS would have been replaced by something . All macOS is is just a different window manager (to borrow a Unix term). Windows and Linux probably be more dominant . macOS is a better system than classic macOS when you realize you still have access to the NeXT internals and even many applications in utilities are really GUIs on top of command line utilities and you can roll back many features…
The facts are: The only other contender was BeOS, after Talligent flopped and Copland imploded.
But Louis-Gassée overplayed his hand.
Source: all of the (other) Steve Jobs books