As a Software Developer, the Document Object Model (DOM) is one of the most important concepts worth understanding.
You're 100% correct. If one is doing software for the web, one should be able to understand DOM and have basic ideas on how to traverse it and manipulate it.
The DOM API is huge and most of the times we just use few APIs. We don't need to learn them all but it's OK to know they exist to grasp our possibilities in the web browser.
Thanks for sharing, Edidiong :)