Is being born with natural intelligence the only way to succeed in college?

Based on the OP’s words it seems that they think that you need to have all "A"s in order to be considered successful in college. For the vast majority of students this will not be the case, especially in situations where grades are curved to give a certain number of each grade.

Also, you are probably not seeing the enormous amount of work that goes into seeming like “naturally smart” “fast learners”.

I am in my last quarter of undergrad and have accepted a graduate fellowship at a top-ranked PhD program in my field, where on the tour I could not contain my excitement about all of the cool stuff that was going on. While my GPA certainly helped get my foot in the door, it was my research experience, communication skills, knowledge about the program, and pure uncontrolled joy at being invited to interview that, it seems, sealed the deal. Not one person the entire week even mentioned my GPA.