That's right - immutability enables equational reasoning, where it becomes possible to actually reason through a program just by inspection and evaluation in one's head, since the only context one needs to load is contained within the function itself - not the entire trace, where anything along the thread of execution could factor into your function's output, since anybody can just mutate anybody else's memory willy-nilly.
People jump ahead using AI to improve their reading comprehension of source code, when there are still basic practices of style, writing, & composition that for some reason are yet to be widespread throughout the industry despite already having a long standing tradition in practice, alongside pretty firm grounding in academics.
In theory it’s certainly right that imperative programs are harder to reason about. In practice programmers tend to avoid writing the kind of program where anything can happen.
> In practice programmers tend to avoid writing the kind of program where anything can happen.
My faith in this presumption dwindles every year. I expect AI to only exacerbate the problem.
Since we are on the topic of Carmack, "everything that is syntactically legal that the compiler will accept will eventually wind up in your codebase." [0]
[0] https://www.youtube.com/watch?v=1PhArSujR_A&t=15m54s