If violence doesn't solve your problems, you use not enough violence.
Also if you don't implement web standards, it's doesn't mean that nothing works. Adblock and noscript break web standards, but people use them just fine, they actually make web work better.
>A massive project like that will have massive code complexity, which leads to enormous number of security holes.
Presumably much of that is in network protocols like heartbleed, which has little to do with something like html parsing or google fonts. Also this is in fact a reason for a new browser engine: Chrome and Firefox lost security, because no matter how much they fix, they still have holes.
>If you don't use Rust, then security would be so bad it's not even funny.
Proofs?