What is the practical difference if the OS provides your general-purpose sandboxed runtime instead of the browser? The browser is already a product being developed by the same organization as the OS for a significant chunk of people.
iOS -> Safari
Android -> Chrome
Windows -> Edge (based on Chromium, so fixes in Edge make their way into Chrome too)
iOS -> Safari
Android -> Chrome
Windows -> Edge (based on Chromium, so fixes in Edge make their way into Chrome too)