I am a Drupal developer since 2008 with the version 5, then 6. Today, I mainly develop in Drupal 8, and still a lot in Drupal 7. But what does "Drupal developer" mean ? There are in facts 3 main fields of competence : the Drupal developer so to speak, the Drupal site builder and the Drupal themer.
As Drupal developer, I develop custom Drupal modules for your site. I look how I can use the API of Drupal Core and those of the main contrib modules : Entity, Fields, Views, Forms, Rules, Migrate, Webform...
Knowing how to develop your features while taking advantage of the existing code in the Drupal ecosystem, and in a future-proof way taking into account Drupal's roadmap, that is the main competence of the Drupal developer.
Being a Drupal site builder, I build sites with Drupal while using at its best Core and the contrib modules. A good Drupal site builder has to design the site architecture in an evolutive way, to anticipate any potential growth. He has to know Drupal's roadmap and get inspiration from it to have a vision of the future.
A Drupal site builder has to be able to code a minimum as well, and know the hook principles of Drupal, in order to connect together functionalites of different modules.
There is a "Drupal way" which garantees more performance, security and evolutivity. A Drupal themer must know the templates system of Drupal, its language (PHP and Twig since Drupal 8), as well as the preprocessing functions.
For work examples, contact me, because what I could show would not be representative. Indeed, I signed some confidentiality clauses, 99% of my code is never publically released and some web sites I worked on are still in finalization.
Unfortunately, I can't allocate as much time as I would like to share as much interesting information as the information I'm consuming. But from time to time, I can publish an article on my blog. Enjoy your reading!