This a major advance.
Did you notice during your explorations of the earlier DHTML that they required convoluted scripts or parallel scripts or sometimes even parallel pages in order to accommodate dynamic effects across browsers?
In contrast, with DOM, a streamlined script will work once for all ~ across the standards-compliant browsers ~ and much more can be achieved. Much more can be achieved, because any element in a document can be changed dynamically with DOM, any element from top to bottom of a document.