we have khelpcenter on the ISO (technically I think kf5 will open a browser if khelpcenter is not installed).
it does however depend on kdoctools which depends on a whole bunch of large data packages such as sgml and docbook-x*.
we could drop khelpcenter, or we could look into why it depends on kdoctools and if that really needs to be installed by default (I am guessing it does because apps install docbooks instead of htmls IIRC)
so, basically devise an action or in-action plan of how to refine the disk cost of khelpcenter.
(mind you, the disk cost of storing html renders of all documentation + translation is higher than the xml/xsl/sgml stuff is)
oh and lastly: it also needs xapian for indexing. so overall, perhaps the best approach would be to drop khelpcenter from the ISO? probably needs talking over with the plasma team but I am guessing since khelpcenter is in apps and not plasma the plasma POV would be that it is not a core part of the experience