> What if Godot stops the development?

You can also use the old version. Also others can take it from where they left off, since it’s open source, as it's has been pointed.

And this is exactly my point.

The sarcasm wasn't obvious.

You can also use the old version, it's not like an old unsupported version of something is any different for open and closed source

They are different, open source is obviously better in that scenario.

Except Unreal is also open source in the sense of them providing you full source code access & documentation on how to build it.

That isn't what open source means. Open source means that you can make changes to the source code and distribute it.