Atticus admits that even in our society not all men are created equal. What is his meaning?

Atticus is referring to intelligence and capabilites. People have different gifts, gifts that are appreciated and utilized in many different ways. Atticus sees people as the individuals they are.

We know all men are not created equal in the sense some people would have us believe—some people are smarter than others, some people have more opportunity because they’re born with it, some men make more money than others, some ladies make better cakes than others—some people are born gifted beyond the normal scope of most men.