This has been a problem since forever with Godot. They like to backport major new features from the development branch to a new minor version of the previous branch. This means the API in the previous branch (3.x right now) is supposedly stable in that it is only extended and not modified. However there are two problems with this:

1. If you use the new extended API is makes the project bound to that version and you lost backward compatibility. So it becomes the responsibility of the user to keep track of which feature are available in which versions and be conscious of backwards compatibility, instead of just sticking with a major version like you can with basically every other software in existence.

2. It’s not even true. They modify the existing API and break projects all the time. The movement functions of the kinematic body classes have been changed at least three times during the 3.x cycle.

So you’re right, the API is not stable, but you won’t get far with criticism from a professional software standpoint in the community (have a look at the demographics listed in the recent community poll for some insight as to why).

Ultimately because of the relative instability of the API, I think this tool will be useful.