I don't see this implied assumption anywhere: smarter simply means smarter.

But, I have to counter your claim anyway :)

Now, "good" is, IMHO, a derivation of smart behaviour that benefits survival of the largest population of humans — by definition. This is most evident when we compare natural, animal behaviour with what we consider moral and good (from females eating males after conception, territoriality fights, hoarding of female/male partners, different levels of promiscuity, eating of one's own children/eggs...).

As such, while the definition of "good" is also obviously transient in humans, I believe it has served us better to achieve the same survival goals as any other natural principle, and ultimately it depends on us being "smart" in how we define it. This is also why it's nowadays changing to include environmental awareness because that's threatening our survival — we can argue it's slow to get all the 8B people to act in a coordinated newly "good" manner, but it still is a symptom of smartness defining what's "good", and not evolutionary pressure.