This is somewhat more complex for the developers of websites but dramatically less complex for the developers of web browsers, and that is where we really shoul

This is somewhat more complex for the developers of websites but dramatically less complex for the developers of web browsers, and that is where we really should be caring: the complexity in the browser leads to both increased attack surface and nigh unto guarantees there will only ever be a single good implementation of the browser. Both standards and security critical systems should be easy to build and easy to reason about.