Funnily enough though (and this might just be my lack of skill in iOS development) I always find the UIKit components surprisingly tough to customize.
This was still a great case-study though! It’s good to have concrete evidence that the performance side of things isn’t an issue
Good - apps should look and feel like the platform.
I would do silly things like clickable image views to get the style right if buttons don't provide the necessary customisability, were I in the author's position. I don't think anyone would be happy with that.
I'm all for platform consistency, which there is very little of these days, but for every API you restrict someone will find a good reason to work around it and that's where the ugly hacks come in.