Wouldn't this apply to today's Apple?
The examples of IBM and Xerox were truly dominant in their day.
I'm not going to get into the definition of "monopoly" here. But there's a reason for the "No one ever got fired for buying IBM" quote, and there's a reason that "Xerox" is/was basically synonymous with "photocopy". No one calls an Android device an "iPhone".
Apple captures basically 100% of the market excitement and profit, but not sales or penetration. Apple is not dominant anywhere near what IBM and Xerox were.
So, for me this fails the test of ~"sales and marketing running the company and not bringing forward great new products". Apple is still delivering.
Apple is not all things to all people -- but no one is without choice. I think Apple, and Apple customers, are happy with Apple.
You could argue I'm just saying they're high quality, which may be true, but the software has been degrading and I have no options if I value openness _and_ quality.
I can flip it and mention features that Apple products don't have that I like.
But this isn't actually an argument for monopoly. That just an argument that you like a company more then the other.
Anticompetitive market structure is bad for consumers loooong before it results in an actual literal "only one company in a broadly defined niche" monopoly.