Cross platform toolkits, be it proprietary, one-off like Sublime's, or things like Qt, GTK, WxWidgets, Java Swing, were NEVER considered native. Just because an app is written in C or C++ doesn't make it platform native.
Textmate is a native editor for MacOS. Sublime is not.
And yes, you may think: "Easy, if a GTK app runs on Linux its native, if it runs on another platform, it's not". Does that mean JavaScript apps for Gnome[1] can be called native, because they have officially blessed bindings to the underlying framework/platform and are fully integrated with GTK?
If not, does that mean as soon as you use any kind of binding/bridging technology "nativeness" is ruled out? Think of C++ apps for Gnome, they use bindings…
If yes, we are only left with defining what the "official" way for doing GUI's on a given platform is. Whatever the vendor gives us and preinstalls on its OS? Ok, no Electron, it uses the Chrome rendering engine, that is definitely third party and NOT native!
But… What if I open a WebKit WebView from Objective-C[2] to render my HTML from there and write my logic making use of JavaScriptCore[3] on macOS? Are we native yet? :)
[1]: https://developer.gnome.org/gnome-devel-demos/stable/beginne...
[2]: https://developer.apple.com/library/content/documentation/Co...
Actually, yes, by definition a javascript app written with gobjects is native to a Gnome desktop. It fully integrates with the standards of the system be it text boxes, keyboard shortcuts, general behavior and widget look. The most important, even more than our personal little preferences, is that a native app can be accessed by things like screen readers which is the only way for a person with a disabled sight to use a computer. Anything not written with GTK on Linux is going to be a black box for Orca. In fact webapps would be less of a pain than a compiled app that uses a random crappy cross platform toolkit. While the web's accessibility could do with some improvements, it's still better than the absolute nothing that cross platform toolkit represents.
Sometimes devs put extra effort into making cross platforms apps accessible but they're the exception rather than the norm : https://www.parhamdoustdar.com/2016/04/03/tools-of-blind-pro...
The reason being is that native apps get "most of the work" done for them for free when they use the native tools to make apps, while cross platform apps require a severe amount of work to get them to talk to screen readers correctly.
Android Studio seems to be gaining on that side despite the original platform being pretty poor. And of course Sublime Text is absolutely unusable in that scenario.
Some apps do crossplatform the right way, although they're rare: they have have a platform-specific GUI rather than use a generic cross toolkit. Transmission is a solid example :
The app has a Cocoa, GTK, Qt, TUI and Web end user interface. It's native on all the officially supported OSes. There's a non-native, Qt-using windows port but it's a third party fork and not supported by the main devs.