Oh yes, I agree, DPI settings should be global accross the system as much as possible and copy buffer should definetly work consistently. Generally it's the application's responsibility to implement the tie in to these platform systems - on the interface level that should preferably not be tied inseparably to any UI code).

To me however, this is on a different architectural level than how the UI itself is inplemented (which, technically, is just motion graphics with hotspots, but psychologically is the most important part for most users).

To give credit - Apples human interface guidelines for the original Macintosh were wonderfull in giving guidance where the UI as a concept was bound to be foreign to most. Also, the first commodity GUIs were on resource strained hardware so they could not do everything effectively.

I think we are now at a point where the glowing animated screen is far more familiar to most people and the raw power available on most devices is such the only rational constraint for UI design is that use experience must be understandable to most and that the underlying system must play nicely with rest of the device.

If I have a choice, I'm always choosing native application for macOS. It's eating less memory (because all shared libraries are already loaded), it provides similar experience as other apps (menu bar, context menu), it's usually works much faster (because Objective C is quite fast compared to some interpreted languages). Sometimes I don't have a choice (like Intellij Idea), so I have to live with Java or Chromium application, but I don't like that experience.