Also IMO unless you want to share C++ plugins with others (via GDExtension), if you are making a game with it you'd want to modify the engine itself for any non-trivial functionality anyway. Again, the situation he describes sounds like it would be much better done by writing the reusable controller itself as a node written in C++ inside the engine itself (not via GDExtension) that uses the fast physics API directly.

Basically what he describes is an issue only in specific situations and not something that would really stop someone from making their game.