MSDOS certainly was simple: it was 16-bit, it lacked preemptive multitasking, and each program was limited to 64kB of memory (that other processes were not prevented from overwriting)!
MSDOS also worked perfectly adequately as the centerpiece of Windows 95 and 98. Of course working is important only to users. And who gives a damn about THEM? (Unless they get fed up enough to leave)
Oddly enough Microsoft's stock price stopped rising about the time that NT started to replace Windows 9. And the rather widespread dislike of Microsoft started about that time.
Just coincidence, I'm sure
BTW, the overly complex OS (relative to current low end device capabilities) is only one of the problems MS faces. And probably not the largest. The multitude of poorly documented and idiosyncratic APIs is probably a bigger issue since the principle reason for selecting Windows is likely in many cases to be compatibility with old applications. If Windows 2016 can't support the software some dude wrote for you in 1996 to control your packaging machinery or deal with your peculiar audit requirements, you probably aren't going to buy Windows 2016.