> it is factually and objectively an esoteric and unusual case.
Sorry, but your unsupported opinion is not "factual and objective".
> If your argument is that all type systems are bad or deficient
I said no such thing, any more than the article did. Again you are attacking a straw man. (If you had said "limited in what they can express", I might buy that. But you didn't.)
I think I've said all I have to say in this subthread.
It's factual and objective that billions, if not trillions of lines of Java and Go have been deployed and the language still cannot express "supports the + operator" as a type constraint. In production, non-academic settings, people don't generally write code like that.
Again, this is an esoteric limitation from the perspective of writing code that runs working software, not a programming language theory perspective.
How many of those lines of code would have benefited from being able to express that type constraint, if the language made it possible?
You have no idea, and nor does anyone else. But that's what you would need "factual and objective" evidence about to support the claim you made.
By your argument, anything that programming languages don't currently support, must be an "esoteric limitation" because billions if not trillions of lines of code have been written without it. Which would mean programming languages would never add new features at all. But it's certainly "factual and objective" that programming languages add new features all the time. Maybe this is another feature that at some point a language will add, and programmers will find it useful. You don't even seem to be considering such a possibility.