Blackrock has thousands of funds, hedge funds, ETNs, subsidiaries resulting from acquisitions which have their own funds. It still matters that they are all under the control of Blackrock and this single entity may drive decisions at the board level through their different vehicles.

They basically own 10% of the DAX. Which is a massive concentration of power over german companies (and it must be similar in other countries).

To the point that if I was a regulator I would question whether it is ok to have a single entity (and the likes of Blackrock) have that much control over the country's corporate landscape.

It looks like they differ based on geographical location and how they are regulated. Two in Germany, two in the UK. Two are asset management companies, two are advisers.