iOS doesn't come as 100mb cellular downloads, so that isn't really the same kind of issue. There are many reports about showing how it's slowly coming into wider spread use at Apple.

For me the lesson is that just because a new technology/language is out doesn't mean you should jump on it. Things need time to mature, and if you're Uber, you can't risk having half of your income rely on something new. Compilers, linkers, and programming languages (and databases and OS kernels) take years to mature. Hell, just earlier this week was a post about diagnosing a 21 year old bug in the Linux networking stack for rsync of all things.

I'm quite shocked that enough experienced people felt that level of confidence. In earlier versions of Swift I personally experience slow compiles and that was on a not terribly large code base -- no where near Uber. That alone should have been a big clue of the state of things.

More like Uber spent too little time trying to keep their app development process manageable.

Uber doesn't have any pressure to have a reasonable tech stack because they don't have to be profitable (because they're an investor charity). On the other hand, having a fancy tech stack helps with recruiting.