Since the first browser war between Netscape and Internet Explorer, web browsers have been using features as their primary means of competing with each other. This strategy of unlimited scope and perpetual feature creep is reckless, and has been allowed to go on for far too long.
I used wget to download all 1,217 of the W3C specifications which have been published at the time of writing1, of which web browsers need to implement a substantial subset in order to provide a modern web experience. I ran a word count on all of these specifications. How complex would you guess the web is?
The total word count of the W3C specification catalogue is 114 million words at the time of writing. If you added the combined word counts of the C11, C++17, UEFI, USB 3.2, and POSIX specifications, all 8,754 published RFCs, and the combined word counts of everything on Wikipedia’s list of longest novels, you would be 12 million words short of the W3C specifications.2
I conclude that it is impossible to build a new web browser. The complexity of the web is obscene. The creation of a new web browser would be comparable in effort to the Apollo program or the Manhattan project.