NeXT gave Apple a mature platform which has withstood the test of time, underpinning multiple architecture changes and adaptation to dramatically different devices. And more importantly, it gave Steve Jobs back to Apple, who orchestrated its recovery from a decline into irrelevance.
I've never heard someone say this before. What's an important missing feature that other OSes had at the time?
Which at the time would have been super super duper important for the just-hanging-in-there Mac user base. (I was one of them. It was just hanging in there.)
The Mac’s professional niche was printing. Prepress. Big press runs. QuarkXPress. And BeOS could barely print, and had no color management to speak of.
It’s unlikely that Apple needed to strip much out of DisplayPostscript in order to rename it DisplayPDF (and then Quartz).