It's a bit more complex than that. I get your point in that one could liken it to a game of Monopoly, and in nature generally 2 animals in the same area don't occupy exactly the same niche, but competitive pressures often lead to diversification rather than extinction.
Windows rules but MacOS is still standing. iOS and Android are both strong. But here's an example that hits close to home for some in the U.S.: Walmart and Target.
Many cities have a Target and one or more Walmarts. They overlap and compete, yes, but they are quite different places. Target seems to aim for a mildly more upscale (mildly class conscious) demographic that values 'chic' stores with aisles that convey more sense of open space (which reminds me of Kmart), whereas Walmart caters to a 'we have scads of everything and pretty cheap' value shoppers. A co-worker once likened Walmart to a flea market.
Neither exterminates the other. They compete but their niches don't completely overlap. Similarly, if my wife and I were in Walmart anymore often they might charge us rent, but I often get 'Primenesia' - where I get enough stuff from Amazon I don't even know what's in a new box till I open it.
While it's true another company may not be able to completely duplicate everything Google does right down to prominent market share, that's okay. They can do some of what Google does in their own special way, while also working in spaces Google's not prominent.
That's a difference from Microsoft way back. Microsoft DOS gave way to Windows, fine. The Word competed with WordPerfect and Excel with Lotus 1-2-3, fine. Then they wrapped their productivity app.s into Office and learned the common interface to outcompete competitors in one package. Oooookay. They didn't want to risk somebody else dominating an important emerging platform, so they released Internet Explorer free that essentially wiped out Netscape Navigator. Quicken was the personal finance big brand, and MS brought out Microsoft Money to compete with that. It seemed like Microsoft was determined to dominate in everything that made much money related to computing, or might involve someone other than them dominating a new sector (hence Windows Phone, and the Zune).
Google has its fingers in some different pies, but they don't seem bent on dominating everything. There was a wonderful comic years ago that said E.T. (the cute yet turd-like alien from the movie way back) in the movie was cute, but E.T. all over your home (the comic showed a restroom with E.T. heads on the wallpaper, toilet paper, etc...) is not. For awhile, it looked like Microsoft was determined to be the 'E.T.' of the computing world.