At the moment, KDE Plasma's metapackage requires the large media-fonts/noto. Adding to that, some websites or applications require fonts themselves such as media-fonts/awesome.
The solution I have in mind is to create a metapackage of all fonts, with USE flags to toggle on or off specific fonts/font packages. Then at postinst the package would spoof what fonts are installed on the system, so that there is a sizeable amount of people 'using' the same fonts.
Regarding size of the package, USE flags for SRC_URI should prevent downloading unneeded fonts.
You may be interested in opening the links below in a container.
Browser Uniqueness Test
Font Fingerprint & Metrics
Eckersley, P. How Unique Is Your Web Browser?, EFF
Browser fingerprinting is a mess but breaking the Operating System is not the way to go, at all.
Browsers should fix this or web browsers would have to be sandboxed (which is effectively what QubesOS is about for example).