Many people feel that way, but it had multitasking, its own APIs, its own memory management, and so on. Disk access was still handled by MS-DOS, but that was it. I’d say that it’s an OS as it is far more than a shell, but we can also use Microsoft’s terminology from the time, “operating environment.”
Not sure if it's important, but Windows 2 is still fundamentally a graphical shell on top of DOS. I think the Unix parallel would be: is the X Window System an OS?
I think about this quite often. OS/2 was amazing. It deserved to win. Honestly, the biggest problem at the time was that Microsoft was much more a bunch of cowboys, while IBM insisted on near perfection. The two sides simply couldn’t agree on anything. Microsoft’s “quality” was focused on being “hardcore” where they wanted things to be lean and quick, quality be damned. IBM was more focused on having very few bugs. If that meant it required more hardware, that simply served their bottom line.
The orriginal target processor—the Intel i860, code-named N10 ("N-Ten") and that was what NT was called inisde Microsoft. i860 was a lousy for hosting OS but awesome for graphics. Soon that was abandoned and NT tageted x86, MIPS, Alpha, PowerPC, Itanium, x86-64 and ARM coming in later releases.
Sadly that means over a quarter century of windows on ARM and it's still not right. Sigh.
macOS and Next Step rely on BSD and the Mach kernel. Android relies on Linux and the dalvik jvm.
Is Windows 95 an operating system ? If not why not. After all it relied on MS-DOS also.
Sadly that means over a quarter century of windows on ARM and it's still not right. Sigh.