Way back in my angrier days when I would have spelled Microsoft as Micro$oft The Evil Empire, I would have totally agreed with you.
I've since revised my opinion. The reason is counterexamples of other wildly software that didn't need operating systems to be successful like Intuit Quicken, Photoshop, Duke Nukem games, etc. If others can sell millions of copies without an os to run on MS-DOS, Microsoft itself can too. Also MS-DOS & Windows dominance doesn't guarantee success because MS Money lost to Intuit's Quicken.
For example, with MS Word, was it successful because of Windows or was it better than WordPerfect? Sure, Windows is a part of it but MS Word was actually easier to use and crashed less often the WordPerfect-for-Windows. Wordperfect-DOS wasn't WYSIWIG. Wordperfect-DOS required memorization of function keys F01 to F12 to bold and italicize. MS Word early versions[1] had obvious buttons for bold and italics.
Now that Microsoft is weakened by iPhone/Android and Amazon AWS, I think I'm able to look back at MS in a more detached perspective. I now think they did amazing work in the 1980s and 1990s which got later overshadowed by the ugly "browser wars" and antitrust lawsuit.
[1] https://tmft.files.wordpress.com/2014/09/krnl386_004.png