But I seriously doubt that programs would benefit much from these micro-optimizations - there are rare and unfortunate cases where indeed there is no one single bottleneck for a program and thus there is no simple way to improve performance, but the vast majority of programs spend all their life in a tight hot loop, and anything else doesn’t matter in the slightest - hell, as mentioned C gets away with as many linked data structure as they want, but writing those in goddamn bash would suffice as well.
(I'd guesstimate that micro-optimizations would go a very long way in improving performance of nearly every program anywhere, but I don't have much data on that besides the couple projects where I've tried to care about performance, and having achieved pretty decent results)
Unchecked operations are acceptable if your code has a single hot loop, but if you have a hundred small functions, each taking 1% of the time, you probably won't carefully examine every stdlib function each of them uses and write code to "work around" every unnecessary thing the stdlib does.
Yes, that's a ton of micro-optimization, but micro-optimization can bring a ton of speedup, so I'll take whatever makes it simpler (or not needed in the case where you already know what will happen due to having written it)