The norm in HTML and many other applications (e.g., Word) is that bullets in lists appear differently depending on how deeply the list is indented. HTML's norm is:
*Solid disc on first level.
*Open disc on second level.
*Solid square in third and deeper levels.

Confluence instead forces a solid disc on all levels in the HTML output. Curiously, Confluence correctly provides differentiated bullets in PDF and Word exports.

I'm sure I could hack something (CSS? theme?) to fix this, but the default behavior of well-designed applications never changes norms unless there is value in doing so.

There is no value in overriding useful, differentiated bullets with more opaque, homogeneous discs, so the default HTML behavior should have been preserved.