Given that our brains have been under heavy evolution, there's no particular reason to think we're at a local optimum.
The environment we've evolved for is not the one we are currently in. What was adaptive 1,000, 10,000, or 100,000 years ago may not be what we need today.
Your definition of "optimum" and your genes' may differ wildly. For example your genes build disposable bodies for the same reason humans build disposable cars: there's no sense in working ever harder to keep the old model going when making a new one is easier.
On the other hand, I've got a similar sentiment from a different perspective: it is surprisingly easy to to FUBAR an evolved system. We're still trying to figure out what effects electric light has on humans. [1] Anybody who thinks they've figured out all the subtle effects of a drug like this is fooling themselves.
Humans have already stepped outside the boundaries of natural evolution. We make casts and hardware for broken limbs; form societies and specialized communities; use drugs to resolve medical issues in individuals that evolution would've killed off. Although as a species we probably rose to dominance by being long-distance runners, most of us can't run a marathon today, because we no longer need to.
Likewise, evolution didn't make humans naturally better at living in cubicles focusing on a tiny device for many hours a day over the course of the last 50 years. The natural wiring for human neurology is still geared towards being aware of our environment, distracted by sounds and sights and things going on, because that's how you survive sneak attacks from predators or spot camouflaged prey.
It's smart to be skeptical of anything claiming to be a miracle cure, but not on the basis of some kind of spooky evolutionary action. Rather, we haven't yet gotten a great track record of coming up with chemicals that can do only one thing to our brains without upsetting some other aspect of our neurochemistry, and that's largely because the brain is wickedly complex and only recently are we starting to make some progress in understanding how it works. I have no doubt that one day we'll be able to fine-tune our own neurochemistry with few side-effects, but today might not be that day.
Even if it was a thing, it has your species interests at heart, not you.
There is a lot to the article and you should take heed it's the future, like it or not.
But if you want a warning sign on Modafinil as per the article the drug came out in 1998, it has been and is still is fairly easy to get, why is it not bigger than it is?
These drugs are still just rough tools, the new batch are coming soon, but Modafinil is not "Limitless"