While I don't disagree about the fact it will likely cause a split similar to Angular, they seem quite explicit about the reasons (not to scratch the itch of the framework's designers).
For me, working in a large project with TypeScript vs one in vanilla JavaScript makes all the difference in terms of how maintainable it is. The number and the nature of the tests I need to write for such project changes, the IDE tooling available makes development much more pleasant, and I generally feel like it is harder to write code that is buggy, because a large amount of potential errors are avoided through use of the type system.
Whether or not they've made the right decision with this split is a different question that I can't answer.