As you point out, many of these features are dependent on how well they're handled by the application developer. If Unicode were "just" about rendering pre-made

As you point out, many of these features are dependent on how well they're handled by the application developer. If Unicode were "just" about rendering pre-made glyphs consistently it would not be nearly so hard, but it aims to do more - sorting, capitalization, string length - and that's also why it tends to fall over in production systems. Nobody is ever going to get Unicode completely right, just a subset of it for the languages they've successfully localized. The simplest character encoding you could hope to work with is something like a single-line calculator or vending machine display - fixed-width, no line breaks, just the Arabic numerals and maybe a decimal point, some mathematical symbols, or a limited English alphabet to display "INSERT CASH". Any featureset above that produces issues. Just line breaks alone are responsible for all sorts of strange behaviors. I think it's a bit magical that we've managed to do so much with text given the starting situation. At each step - from early telegram encodings through the proliferation of emoji - the implementations had to codify a thing that was previously left open, develop rules around its use, etc. We've made language more systematic than it ever was in history, for the benefit of machines to parse and process it.