> are we now arguing Google has a monopoly over google.com? It gets a bit weird
I don't know anyone who's arguing that. But I do see people arguing Google having a monopoly on search. In a lot of domains, a business can be created or destroyed entirely on their Google search rank.
Even if Google search was broken off to a standalone company, it would still have a monopoly on search.
The competition just isn't as good at search. Bing has been around for a long time and has managed to gain less than 10% of market share, even though almost everyone has heard of it.
That's only if you rig it by choosing the market to make it turn out that way. They aren't a monopoly in every market they are in. They're monopolies in specific markets. No company has ever been a monopoly in general, except perhaps the Soviet state but even that isn't strictly true.
Search? Google. Online retail? Amazon. Video hosting? Google.