Don’t be overwhelmed by the architectural changes introduced with Drupal 8
Drupal 8 embraced technologies from outside the Drupal ecosystem to modernize the way it works. It offloaded functionality to external components which already solve the same problems like routing and templating, embraced dependency injection to configure services, and uses object-oriented programming to better structure modules, plugins, and core libraries.
As a Drupal developer, you need to be proficient with working with objects, classes, and methods. You need to know how other PHP programmers use tools like Composer. You need to see how to integrate 3rd party components from Symfony and other frameworks in your own code. To build custom modules or integrate external APIs, you have to have a firm grasp of dependency injection and how to design and use your own classes and objects. Finally, you need to stay up-to-date on testing and deployment practices.
Attending php[world] will help you leverage the lessons learned by developers in the PHP community to manage and deliver large-scale web applications successfully in your own Drupal projects.