"only MacOS managed to survive (barely) because it was so entrenched and Microsoft at some point become complacent and have not killed it when it had the chance."
Remember that Microsoft didn't "not kill" Apple -- they funded Apple when it seemed like Apple was dying. Perhaps that's complacency, or perhaps it's something along the lines of picking whether you want to fight a small incompatible competitor or the antitrust folks. (Who could have guessed at the time that Apple would produce the iPhone craze.)