Normal en keyboard layout's just not good—too hard to type various characters that occur in English text, some uncommon-but-not-rare and some downright common (—, ü, å, ¢, °, •, é, ç, ñ, and so on, and sure, a bunch of those are for loan words, but that's still English).

Linux has good ones, I've just never seen one as the default; if you just click through the "happy path" you'll have a crap one, and there's little guidance on which you should pick if you need to, like, actually compose text in your native human language, so the user just has to know in advance or go look up which one to select.

Mac's default, meanwhile, is (at least) nearly as good as the best Linux has, so you can start fluently typing English without having to fiddle with settings or memorize weird number sequences (sure, there's still some memorization, but much of it's simpler and closer to making sense and far more guess-able than, say, a four-digit string of numbers). Last I checked, Windows gets this wrong, too. Why either of those operating systems does that, I have no idea. That it was even incorrect didn't occur to me, somehow, until I switched to Mac and was like "why isn't the default at least this good on every platform!?"

Linux has the "Compose key" concept that solves 99% of what you list in your claim. You have to map it to some physical key on PC keyboards, though. All the DEs I checked let you do this in the settings. My only complaint is they they don't allow out-of-the-box to assign it to the Insert key, which I never use in its intended function.