[blobs]

Whatever words you use, it simply conflicts with basic JS and is a serious flaw.

  const cat = new Cat();
  if (cat instanceof Dog) console.log('this should never be possible!');

What is this strange protective behavior towards TS, can we stick to logic please?

[redmorphium]

instanceof checks the prototype chain, which is a different concept from type. Prototype chains are dynamic and exist at runtime, while Typescript types are a static concept.