This is the sort of absolutism that is so pointless.
At the same time, what's equally frustrating to me is defense without a threat model. "We'll randomize this value so it's harder to guess" without asking who's guessing, how often they can guess, how you'll randomize it, how you'll keep it a secret, etc. "Defense in depth" has become a nonsense term.
The use of memory unsafe languages for parsing untrusted input is just wild. I'm glad that I'm working in a time where I can build all of my parsers and attack surface in Rust and just think way, way less about this.
I'll also link this talk[1], for the millionth time. It's Rob Joyce, chief of the NSA's TAO, talking about how to make NSA's TAO's job harder.
[0] https://arstechnica.com/information-technology/2021/01/hacke...
I'm beginning to worry that every time Rust is mentioned as a solution for every memory-unsafe operation we're moving towards an irrational exuberance about how much value that safety really has over time. Maybe let's not jump too enthusiastically onto that bandwagon.
For example, in garbage collected languages the programmer does not need to think about memory management all the time, and therefore they can think more about security issues. Rust's typesystem, on the other hand, can really get in the way and make code more opaque and more difficult to understand. And this can be problematic even if Rust solves every security bug in the class of (for instance) buffer overflows.
If you want secure, better use a suitable GC'ed language. If you want fast and reasonably secure, then you could use Rust.
I don't disagree with the premise of your post, which is that time spent on X takes away from time spent on security. I'll just say that I have not had the experience, as a professional rust engineer for a few years now, that Rust slows me down at all compared to GC'd languages. Not even a little.
In fact, I regret not choosing Rust for more of our product, because the productivity benefits are massive. Our rust code is radically more stable, better instrumented, better tested, easier to work with, etc.