This is not the case for Vangard. The model for vangard is that it is owned by its constituent funds, which are owned by the investors in those funds. That's why vangard has so many devotees, boggleheads, etc.
Vanguard and Black Rock are both public companies. You can see who the largest shareholders are 🤷
Discussion
It's true that it's a pretty unique model, but doesn't mean the information doesn't exist. The largest investors in Vanguard funds are almost certainly going to be entirely institutional investors. Those would be the "shareholders" of vangaurd group under their unique model