Sublime doesn't use native platform UI toolkits. They ship their own version of Skia (same as what's used in Chromium) and have their own UI toolkit for the editor rendering.
Frankly, I think the MacOS HID has been dead since Mojave. At some point, developers realized that Cocoa wasn't enough for most apps, and it was an awful lot of work to put into an app that would only be used by a fraction of their customers. Currently, the definition of "native" on MacOS is that it uses loosely the same keyboard shortcuts as your other programs, and if you're lucky then it integrates with your global menu. In the age of webapps and cross-platform development, there's simply not a way that MacOS' approach works. Even niche toolkits like GTK solved this problem better than Apple, which makes it even more mind-blowing when I see Mac developers defend their build system.
Walled-gardens lead to sticky situations like this, where volunteer-driven efforts are more developer friendly than first-party offerings. I weep for the Xcode users who don't know what it's like living on the outside.
AppKit only comes up short in that it’s not built to have its appearance changed dramatically and of course that it’s tied to macOS. If you need cross platform that’s a legitimate limitation, but as noted before brand driven UI design is far from a need.