The monopoly that Apple does not have on smartphones as a whole, and the consequent constraints on its ability to dictate the functionality of the mobile web, to capture mobile web and app advertising revenue, etc.
That's the success of Android.
A duopoly between two non-Google vendors (especially if they were effectively two monopolies in distinct market segments) would scarcely have been better for Google than a non-Google monopoly, so even if a low-end smartphone market existed and was substantial without Android, and your perception above in regard to Apple staying out of it without Android is correct, that doesn't materially change the nature of the success of Android for Google.
https://www.reuters.com/article/us-oracle-google-lawsuit/ora...
The first line at your link: "...revenue of about $31 billion and profit of $22 billion..." Again, fake numbers, but wow that's profitable.
22 billion in profit in almost a decade for having 80% of the market is peanuts.
Google has paid more than that to Apple for being the default search engine on iOS for the same time period.
Much of your analysis in this thread suffers from a form of wishful thinking. I suspect you are a fan of "iPhone" devices.