In games like CoD, I would bet iron sights are supposed to less good. That way they can push players to leveling up guns to get better attachments. If they happen to sell a gun in the Mtx store that has a really good sight/scope even better.
"in this essay"
The article you've written is not an essay. It is at its top, an opinion article
And as Vodulas points out, they generally serve as a game mechanic. Either you are recreating set guns from history or it's lower level gun meant to be a bit crappier.
What even is this articles point? Iron sights are crappy? Yeah, we know, that's why that was improved upon and they barely exist on IRL guns today