Actually it would have been WindowsNT (yes serious).
OS-development under C= has allways been seriously underfunded and such were the results.
When C= bought Amiga most of the basics of the OS had allready been done and C= only made sure the biggest holes were filled in the cheapest/fastes way possible (the dreaded Tripos-DOS comes to mind).
1.1 was just a quickfix to allow for PAL-Amigas, 1.2 had some serious bugs removed, and 1.3 offered little beyond autobootsupport a basic Shell and support for more than 512k chipmen.
2.x was the 1st real update and that happened 5 years after C= bought Amiga.
Or in other words, if C= had started on the same basis as MorphOS did 10 years ago they wouldn't have gotten much further ...