It's purchasing power though. Optionality not projectable power. He can only sell 4% of the bitcoin supply once.

The power is not in his hands at all. MSTR and it's Bitcoin are a regulated entity owned by the shareholders. Even if 4% of the supply was owned by an individual, how is that a risk? The worst that can happen is that it was sold all at once and the price dipped briefly. Big whoop.