Goal

Let's use this issue as a meta issue to track fundamental software design issues within Kibana.

• Find examples of our code which people have found confusing, e.g. Courier being confusing/difficult to use, @weltenwort mentioning problems with searchSource in Discover.
• Identify why they're confusing, e.g. anti-patterns, code smells.
• Suggest solutions via refactoring or redesigning.
• Link out to relevant issues and PRs.