Jeffrey J Kontur
I am a paygrade 20 in State goverment, which I think is roughly equivalent to federal GS 14-15. The premise of your question is a little too broad. Many times these days people with highly specialized skills may be brought in at higher paygrades mostly for salary considerations.
Being completely honest, that was the case with me. Though I did have supervisory experience and management skills and I even continue to develop those, they were not a primary factor in determining paygrade. In fact, my continued development is for me personally and has almost zero effect on my job performance or future promotability.
That said, outside of technical circles I think there is an approximate correlation to time in service and skill set differences. Experience is a great teacher and the more years you put in doing something, the more different scenarios you know how to deal with so the more skills you have.
That’s the norm. Looking at exceptions, we all know of people who have been in their jobs for decades and made unimpressive advancements up the paygrade scale. We also know of people who study hard, work hard and simply rocket up the scale.