https://ardour.org was first ported to then-OSX in 2006. Almost nothing in the codebase that relates specifically to now-macOS has changed in that time.
XCode is a tool, not a platform. Cocoa is the platform, and it changes very little and very infrequently.
When we first ported Ardour to OSX/macOS, it was abundantly clear that XCode was a non-starter in terms of technology, partly because it was single platform, and partly because its scope was too large - as Unix-based developers we understood the merits (and occasional pain) of more modular toolsets. So I found a handy guide to writing "nibless applications" that completely removed XCode from the picture (along with some Cocoa boilerplate code that isn't actually required). As a result, we've continued to interact with the stable API core of Cocoa, even as Apple dither around the edges.
Apple (and Microsoft and .... ) are not your friends. They want you to build software for their platforms, but beyond making that possible in some way, their incentives do not align with yours in any substantive way (partly because they make software too, and have their own API goals and needs that may/will conflict with yours). If you don't understand this, you're inevitably going to have the sort of experience you describe above.
By the way, a blog post on how to create Nibless apps would be invaluable.
I'm not sure if this is the source I used, because the date is a little late, but it seems very thorough and excellent:
http://lapcatsoftware.com/blog/2007/05/16/working-without-a-...
Qt is native in that sense, just as much as any other toolkit designed for the same purpose.
But the number of Windows native app APIs is insane, and every year I try to learn how to create an XCode basic app and it’s different. Creating a simple app with HTML and JS however is the same as it’s always been.