I've been building websites for 10+ years as well, and I can't tell you how many hours I've wasted on workaround to make something trivial work in Safari that required no work in other browsers. I've also run into some pretty gnarly animation performance issues over the years.
That being said, Apple has clearly upped the focus on the browser in the last two years, and they are shipping a ton more features and fixes in each update, so kudos to them for refocusing as of late.
HoloKit, originally a Google Cardboard-like AR device for the iPhone, has been relaunched as a more premium $150 iPhone accessory. Unfortunately no SDK available anymore (for now at least).
I'm a developer myself and use Apple both professionally and personally. I hear the walled garden excuse frequently from those who choose not to use Apple products, but honestly I don't run into limitations often on macOS. I have to ask - what is it that you're trying to do that makes you feel as though macOS is a walled garden? Short of really serious kernel extensions, I don't find myself pressing up against a walled garden on macOS.
That being said, iOS is absolutely a walled garden, though I rarely find myself in need of something that it doesn't accommodate anymore (with the exception of WebXR, which isn't exactly popular yet). But Microsoft doesn't have its own mobile OS anymore, so not sure this is analogous.
That being said, Apple has clearly upped the focus on the browser in the last two years, and they are shipping a ton more features and fixes in each update, so kudos to them for refocusing as of late.