I'm sorry I don't understand your argument at all. What does lack of UB and memory safety have to do with simplicity? Those are very complex features of Rust which require a very complex compiler in order to achieve. Also Rust is notorious for having a steep learning curve, and it takes time for even very experienced programmers to become accustomed to it.

> a thin abstraction over assembly

Do you agree that this statement implies 2 things

1. The compiler isn’t doing anything unusual or unexpected. It applies only basic, easily understandable transformations from C to assembly

2. An intermediate C programmer would be able to guess correctly most of the time what the generated assembly would look like. And thanks to this, such a programmer would be able to avoid most footguns.

But the compiler does unusual/unexpected things, and it’s hard to guess what assembly will be generated or what that assembly does, it’s not a “thin abstraction”. Would you agree?

I don't think this is the best way to understand this. C has been around for 50 years at this point, and there has been an enormous amount of investment and advancement in the realm of C compilers in that time, which has naturally resulted in complexity and esotericism in terms of how actual mainstream C compilers work. But that's not a metric of language complexity, it's an artifact of a half century of work on the topic.

I think a better metric is: an average CS grad with a little bit of background in compilers and assembly could reasonably be expected to be able to write a naive C compiler which covers say 80% of the footprint of the core language on their own in a matter of weeks.

What do you think is the size of the cohort of people who could write a naive Rust compiler, with borrow checking, ADT's, traits and non-lexical lifetimes? Even without some of the fancy bits like async you're already talking about grad level CS topics at the very least.