And nobody is proposing to do this. The OWG discussions I’m aware of centered around whether to host OpenMapTiles, geofabrik’s ShortBread, or some other community schema to be invented. If a style wanted to use some data that wasn’t in a hypothetical OSMF-hosted vector server, at that point they’d have to run their own server that’s customized to serve the data that they care about.
But to your point, hosting a generic tile server where every style gets the same data whether they need it or not is fundamentally inefficient compared to an equivalent raster, unless that vector schema is specifically tailored to what the client style actually uses.
That said, the proposed OpenMapTiles style doesn’t really suffer from these criticisms because the style is intended to show off the data that’s in OpenMapTiles. The one exception is language information, which is encoded in the tiles whether the client chooses to display them or not.