> optimizations applied at different levels of the stack

That's because it's just "guess and check" not some deep universal insight.

It's closer to "we can make this highly parallel for not that much cost, but we struggle to use that concurrency. So what if we just guess what the next step is going to be? If we are right we get a big speedup, if we are wrong we just throw that work away". Which I would classify as a notable insight. Doing work that you are 50% certain is useless is not the most obvious thing

Simple optimizations are often the best :)