In vector we output assistive headers into h5's to separate the parts of the UI for users using screen readers to understand.
However we use display: none; on these headers.
Modern screen readers use standard css-capable web browsers. This means that use of display: none; hides content from the very users who are supposed to be seeing them.
WAVE's text overview provides a good view of how this affects the output since they intentionally hide content that is display: none;ed to reflect the reality of screen readers:
As you can see our personal links, namespaces, and actions all just end up as a big mass of unlabeled lists that appear conceptually as part of the page text after categories.