As important as politics and implementation diversity are, if I were to take on the monumental task of developing my own browser I would rather focus on improve

As important as politics and implementation diversity are, if I were to take on the monumental task of developing my own browser I would rather focus on improvements that are actually manageable and useful to me as an independent dev or small team. Browsers are more than just webviews with tabs and a lot of potential in the non-core parts is left unexplored by the major players. And it's not like you're throwing away any effort. A browser isn't automatically worthless "just" because it's built on WebKit the same way an operating system isn't worthless "just" because it's built on Linux.