> The way TypeScript was designed is in fact more promising than older systems like Java. Those systems inadvertently broke type soundness instead of making it a deliberate action.

Not sure what the article is referring to here...

Java soundness issues like array covariance, final field mutability, unchecked generics casts, etc were definitely surprises to many users, but the Java language designers were well aware. They added runtime checking to make sure those soundness holes didn't cause the JVM to crash or violate the security guarantees.

Sure, there were some additional surprises, but I'm sure TypeScript has had many more. (Partly because the TypeScript type system is more complicated, but also because it's not important to get it 100% right -- JavaScript runtimes don't perform optimizations that rely on the soundness of TypeScript.)