I'm a frequent flyer with status on United Airlines.
This "onboarding" demonstration is an eye-opener for me. While I didn't experience any of the issues that this slideshow demonstrated, I now realize that my experience and knowledge with flying United helped a ton to start working with this app. On a related note, I also did not share the same general resentment for what United did on the recent flight to Louisville. Not because of lack of empathy, but again because of experience both good and bad, and also because if I were to be the doctor, I would know my options for getting to my destination in time. After a while, you start forgetting that other people do not share that level of experience and knowledge, and to make this relevant for Hacker News: this is an issue that affects me as a developer too.
That being said and in United's defense, this app has incredibly powerful functionality that's not mentioned at all here. This app allows you to scan your passport and get it "pre-approved" for boarding an international flight, something that can save you A LOT of time at the airport. Furthermore, in case you are affected by "IRROPS" (delays and cancellation) the app can offer you alternatives and rebook you immediately. And there's a lot of other helpful stuff this app can do. Granted, it is still limited in what it can do, and sometimes it can't help you out, but it is a huge timesaver if it does. In short, the United iOS app can be an incredibly powerful travel companion, but it still requires a user that is more educated about air travel than the average Joe.
So as a developer, I do agree that the onboarding experience for inexperienced users should improve and I will look at the onboarding process in the applications that I write. But at the same time, as a frequent flyer, I hope any changes do not constitute merely "dumbing things down" at the expense of the powerful functionality where this app really shines today.