No, the W3C publishes a lot of standards apart from HTML and DOM, and they would still be somehow involved here too.
However, it is indeed sad that the HTML spec is now controlled by browser makers only, and the editors are mostly from just one company.
FWIW, w3c publishes and standardize a lot more than just HTML and DOM. So calling it irrelevant seems a bit of a stretch.
I would also add that having third-parties propose specifications to standardization bodies is a widely established practice. In fact, standards are supposes to reflect industry practices and are a way to establish common ground.