Admittedly, that's a pretty blurry line and I'm not sure it's that easy to quantify what a "real" programming language is supposed to be, without moving the goal posts!
For most games out there, GDScript could indeed be all that's necessary and might be "real" enough to get things done and be a comfy experience.
For others, they are more than happy to bring their own IDE and the knowledge, as well as the ecosystem for their more advanced needs!
While having an extension mechanism for the engine is pretty cool (here's an article: https://godotengine.org/article/introducing-gd-extensions) sometimes you want things to be as easy as just adding a script in the editor and opening it in your IDE of choice.
I think it's pretty cool that Godot mostly caters to all parties here!
Fair enough. I mean, when I use Godot, I use GDSCript... I do like it. It's just not general purpose and I'm ok with that. It accomplishes what you need for most games. And GDExtension or C# are there when you need more...
JetBrains is a billion dollar company that ONLY makes tools lol... Of course they have a leg up.
> I don't see anyone writing a linear solver, or their own networking library in GDScript anytime soon
Wrong tool for the job. That's why GDExtension exists. That's why C# is integrated. Also Godot already has ENet networking integrated into the engine.
GDScript is an alternative to something like Blueprints for basic behaviours that only call engine functions, not a full replacement for real programming languages.