Not saying youre wrong, but you took the wrong project as an example hehe.
Visual code is not open source. Its core is, but visual code isnt.
The difference is what visual code ships with, on top of its core.
Its like saying chrome == chromium ( it isnt ).
Visual code comes with a lot of features, addins and other stuff that isnt in the core.
.net debugger for example, is not found in vscodium ( build of the vscode core ). And there is more stuff i cant think of now but have come across.
Source: been using vscodium for a few months instead of vscode
I know, hence why i said youre not wrong but the example was wrong :p
Also, its more complex than that. Some teams can, some cant. And if they can it all depends on what project or context. The business world isnt that cut and dry hehe