Other traits like height, health, beauty vary and are influenced by genetics. Intelligence varies between species, and is therefore, at least in part determined by genetics.
Presuming that there are only mentally disabled and normal people is the weird hypothesis. The baseline idea should be that it varies just like health and height. Affected by both genetics and outside factors such as malnutrition and injuries.
It could also be that you only need a certain percent of new content to keep eyeballs. Thus, by only showing some new content at a time, instead of all at once (as in a chronological feed), you would increase user engagement time.
I think that the disagreement stems from the difference between what you and him mean by definition.
We use words to describe, and to categorize stuff. But naturally this vague. Everybody undestands if you describe a shirt as blue.or green, but most people would find it hard to describe when one turns to another, where the boundary between them is. So we use other names for that, or describe it as blueish green, or something similar.
To get rid of confusion, handle edge cases, and for other reasons, we define formal defenitions, which are different from the ambiguous idea we have of something.
What the comment you replied to means, is that the formal definition doesn't fit his idea of what is natural. You on the other hand are saying that the formal definition is the only (valid) meaning of the word, and so it can't be good or bad.
Presuming that there are only mentally disabled and normal people is the weird hypothesis. The baseline idea should be that it varies just like health and height. Affected by both genetics and outside factors such as malnutrition and injuries.