Those are a 2D map editor and a 2D animation editor.
Apples and Oranges compared to what the editors in Unity/Unreal/Godot do.
> There's no chance to "make people think" that such things can't exist.
A lot of people in this very thread seem to be under this impression.
> it's that integrated tools are often much more effective when building things out of multiple different pieces
Integration can happen in different ways. Complete integration (aka being made by the same team and tightly coupled) is not necessary for a great experience.
For programming itself we’re already free to choose our editor of choice, and they often integrate quite well. People used to say the same about Visual Studio and C#.
> Custom file formats exist because features differ, and even for similar features, the semantics differ.
There is a lot of common functionality in modern engines. Not to mention that formats can be extended to contain additional metadata coming from customised parts of the editor. And editors can be extended to allow new formats too.
Starting with the automatic assumption that there cannot be a common format is incorrect.