Unlike iOS you can install different browsers on Android directly from the Play Store. These can actually be different browsers with their own rendering engines not just alternative UIs on top of Chrome. Firefox on Android for example uses the actual Firefox rendering engine, not Chrome.
you may install firefox and still will have a lot of time links opened in built-in chrome, on android
Android has over an 85% global market share. And for OEMs, there is NO other game in town, since iOS isn't licensable.
The reason Microsoft got in trouble is because it was not only found that they had a monopoly in a particular market, but that they obtained some of that market share illegally through shady contracts effectively forbidding OEMs from offering alternative OSes, etc... They were then found to have used that illegally obtained monopoly to take over a completely different market in part by bundling IE with Windows and punishing OEMs who sought to including alternate browsers and completely disallowing the removal of IE.