I've actually seen these kinds of very-valuable positions replace by the mythical "TPM", who (unless they are very good) has zero hands-on knowledge and wants n

I've actually seen these kinds of very-valuable positions replace by the mythical "TPM", who (unless they are very good) has zero hands-on knowledge and wants none. They are worse than unhelpful. A good prin engineer gives all the same schedule updates and cross-functional requirements-wrangling that a mediocre TPM would, but also produces useful code examples, coaching, and PR reviews.