They don't need to embed ads into the browser if the websitet that the user will load are already loaded with google ads. They also don't need to replace competitor ads with google ads if there is no meaningful market share by any competitor.

Why should they siphon data to a third parties when they themselves want the data, and its a competitive advantage to keep that data for themselves.

What we are seeing is chrome becoming the new IE where alternatives browsers are not longer allowed on the internet. "You’re using a web browser that is not supported. In order to use [Insert website], please download Chrome for the best experience. Download Chrome here!". (https://www.datanyze.com/browser-support/ie/index.html)