https://www.computerhistory.org/atchm/macpaint-and-quickdraw...
The closest 3rd party app I've found to ms paint is Paintbrush, but that's a bit too primitive compared to paint and it doesn't work that well with retina screens.
PS - I'm familiar with the Spotlight Search trick (and asking Siri) but that is pretty limited.
If you open an image or PDF in preview, just go to View -> Show Markup Toolbar
Or you can choose tools right from the Annotate menu.
Krita, for example, seems popular: https://krita.org/en/
I know nothing about Krita other than its existence. I imagine there are other options.
> hinders the development of other open source apps for the platform.
Filling the same niche as Paint is hardly improving the world. As soon as your Paint clone does anything innovative it fails to fall inside the constraints of Paint.
As a simpler example, any Notepad clone that added, say, tabs would instantly fail to be a Notepad replacement. I'd seriously question how much value OSS competition (consisting of a native textbox and menu bar) is adding to the world. Edit: Just because OSS can compete doesn't mean it should.