shared libraries [ no longer specific to either Rust or Fedora ]

The full move to Harfbuzz is required to properly support modern opentype (TTF and OTF) features, be it latin legatures, non latin scripts, emojis, color, etc. Harfbuzz has two decades of enhancements, fixes and rewriting over the old freetype code it was originally forked from.

High resolution (aka banal 4K screens) is not directly involved, except inasmuch the very old pre-opentype fonts that render worse with the new system, mostly because they were designed around the old system bugs, are useless on such screens (way too small). And also, they look like crap compared to banal vector fonts rendered on such screens: there is a point at which no amount of pixel hand-tuning can compete with more pixels to render fine details. It’s no longer distorted sharp vs blurry fidelity, it’s sharp fidelity vs blocky pixelated that relies on old bugs.