How to advance as a data/analytics engineer or developer?

I am working on dev and data projects for years now. Would I call myself an advanced engineer? Yes and no.

When I started to work on datatasks it was clear to me that I wanted to do the backend services. I have plenty of experiences working with data APIs and pipelines. So it was obvious. 

Due to a bigger consulting project I struggled to find time to develop and the frontend needed the APIs. 

So I hired Yevgen Runts to help with the backend service. And he did amazing work (if you are looking for a great python dev – write to him on LI). 

And what he did was miles ahead what I would achieve.

What is the difference? 
I always developed mostly for myself. So my code was optimized for one brain. But good code is optimized for X brains. 

Yevgen‘s code is so well structured that it can scale easily and a new dev needs few time to understand and work on it.

This is my next level.