The team developing NT had the requirements to fulfill that were never put in front of them, and their result was at the end something in many aspects fundamentally better than any competition. There are of course some aspects that the competition did better too, but that was not enough to win the market.
Whoever really wants to learn more about how it was made, including a lot of details about the humans involved, should read the very good written book
"Show Stopper!: The Breakneck Race to Create Windows NT and the Next Generation at Microsoft" (1994) by G. Pascal Zachary
I can't recommend this book enough. It's a very interesting story and gave me an appreciation for what it takes to do big things in the software industry.
The amount of cool, ground-breaking stuff that IBM has done is severely under-estimated. I wouldn't count OS/2 as a part of that, however.
OS/2 1.3 came out at the beginning of 1990 and OS/2 2.x came out 1992.
By comparison Windows 95 came out in 1995.
So you need to compare OS/2 to MS-DOS, Windows 3.x and the Apple Macintosh systems of that time and by that comparison OS/2 was very good.
In the early 90's I did a lot of development for OS/2, MS-DOS and Windows 3.x and OS/2 had the big advantage that a bug in your code would only crash your program where asd for MS-DOS and Windows 3.x it crashed the OS and required a full reboot.
The fatal mistake IBM made was to hobble OS/2 2.x to the 80286 processor.
By staying with the 80286 processor it meant OS/2 ran really struggled to run MS-DOS and Windows programs and that meant businesses just stayed with MS-DOS and Windows.
If they had just gone with the 80386 processor (like they did 2 years later with OS/2 3.X) it would have meant the end of MS-DOS and Windows 3.x only because that later version of OS/2 ran Windows and MS-DOS programs better than Windows 95 which was still a year way.
It was the OS/2 1.3 release that should have been targeted at the 386 chip.