As recommended here: http://feinstaub.github.io/blog/kde/2016/01/29/view-disk-usage-via-dolphin.html I like to propose "fsview", it is bundled with kde and is the best graphical tool for disk usage in my opinion.
fsview no longer seems to exist as a GUI app, or else is CLI-only. This user interface only makes sense for GUI apps, so I don't think we'll be able to do this.
It exists as a gui app. It is a standalone GUI app AND a kpart plugin. For opensuse it is currently in the package "konqueror-plugins". in my opinion, it is much better than filelight.
Gotcha.