>Further, if there was a simple chemical way to accelerate actual brain processing thousands of times, you don't think evolution would've built it into our brains?
Not OP, but I'd counter that evolution is doing an imperfect multivariate optimization over a pretty big state-space. Even if it might be easy to change one simple chemical and thus speed up processing, the question is whether the speed-up has other costs.
E.g. the brain is already using a lot of energy, increasing processing speed which probably increases energy usage might not be optimal.
We still don't understand sleep well, it could be that if you process faster more consistently you might need more sleep to organize your thoughts and memories, which is counterproductive if you don't want to be eaten. It's hard enough with our sleep requirements to keep up with nature.
A third point is that evolution only needs to find good enough. We're already the apex predator due to our ability to think. Anything above what we currently have might just not be necessary so has no evolutionary pressure.