It's funny because Typescript started out by trying to get ahead of a lot of features and "settling down" to trying to stick to (mostly) only TC39 Stage 3+ features has been a maturation that has been good for the language. It's interesting that Flow seems to be moving the other direction.
A benefit to making it easier to pipeline Typescript inside Babel is that it is no longer entirely on Typescript to transpile every possible wishlist language proposal. This is also why a lot of people preferred Flow because you could just slot Flow checking before or after certain transforms. Typescript is getting better about fitting into the middle of a Babel transform stack so that you might have some basic preprocessing steps of Stage 2 or earlier or non-standards track things that Babel supports before type checking.
(The Optional Chaining proposal for `?.` is currently in Stage 2 in TC39. Indications seem to be that at least some of the Typescript devs are ready to champion that feature in the very minute it hits Stage 3.)
