People are using storyboards for complex UI? I was under the impression that people used the more manual processes with larger teams.

Storyboard references made composing complex UI possible, but IMX there's almost always some breakpoint where it's just less complex to do it with code.

you are right, not sure why you are being downvoted

Almost no large scale app uses storyboards for most of their ui....

I do a mix. The "program by painting" is great for some things and sucks for other things. Unfortunately, programming UIs entirely by text is terse for some things and incredibly laborious/tedious/boilerplate for others (e.g. doing autolayout in code sucks).

So I end up doing both. The problem (and I've seen this for many years with other similar systems), is that you have to become relatively comfortable with both approaches, so you can make informed decisions about when to flip back and forth. When can I do this with IB even though it's a teensy hacky vs when should I just subclass UIView and take over layoutSubviews and friends?

That's been my experience at least. YMMV.

yes, my team have been using Storyboard/xib for 99% Auto Layout declaration, PaintCode for rendering custom components (which can be shown directly inside IB), RxSwift/RxCocoa for MVVM

This is the exact opposite of how I feel. SwiftUI will be much better for that scenario.