To be fair to Apple here (and this was way before my time, so I'm probably mixing stuff up) - Garageband dates to 2004 with the eMagic acquisition and was (iirc) built on top of the Logic Pro audio engine. And back then, you still had to deal with the raw CoreAudio API (if anyone wants an adventure, try finding the documentation for it... you'll have to generate it yourself!) on MacOS. I recently had to dig through the old CoreAudio mailing list and read a book  on the API for low latency stuff, and I'm guessing that in terms of their engine there wasn't much needing change (at least architecturally) to port to iOS. I seem to recall the biggest difference between desktop/mobile versions was the featureset and UI, I think the problem you mention was present even in Logic. You had to get hacky with ES24's key/velocity maps to do what you mention.
From working in the pro audio world for awhile, I've found that other folks in the space just love to talk shop about how they do things. Audio devs are nerds like that. Doesn't always mean people are stealing from others.
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