Unfortunately, this point of view has little merit.

Security is all or nothing. You can't have a little bit of this and a little bit of that. Unless the parts of the web browser that can be "influenced" by external attacker (directly or indirectly) are written 100% in a memory safe language, you simply have no real security but the illusion of such.

And this is how that hypothetical browser fails, and why it will never amount to anything re: security, since it's gonna end up using a gazillion of C libraries, all of them full of bugs and possibly vulnerable to security exploits.

One could say that Rust also fails by allowing "unsafe" code in its core design but it's still too early to see how that will play out.