I believe that the situation you mentioned is the same for every applicant.
Most of the MBA applicants are in their twenties or early thrities, and their positions in company are not so high as to make so-called "GREAT ACHIEVEMENTS".
My thinking is that what matters is not WHAT you write about, but HOW you describe it.
I read an essay from "65 Essay chosen by HBS", and it was about "an important moment of one's life". Below is a summarized content of the essay.
I was sitting in a car during a rushhour in the city of xxx. A poor child came and knocked on the windows of my car. Looking at him, I thought blar blar~.
I was much surprised that this "insignifant" experience (sitting in a car and see a boy knocking on the window) turns out to be a great essay.
Again, I believe that it depends on how you write it, not what you write.
Hope this helps.