I think the biggest risk (if there is one) is they can move the market. If on the extreme end they held 99% of the BTC cap, then they can sell all, or a large portion, of their coin and drop the BTC/USD price. Other than that I don’t really see a risk. I may be ignorant but just my thoughts.
Discussion
No, that would be good for us. There are two attacks - 1 is an attack on our values, the other is an attack on the currency aspect of btc.
We value freedom. Political freedom and economic freedom are closely linked. Economic freedom is far more pressing to most people. Most people have no btc savings. We could succeed in making btc the work currency but fail completely at rebuilding economic empowerment. If these funds become banks that never sell except to make loans, then all btc flows back to banks. They effectively own the world.
If they remain only funds and people speculate on dollar prices, fiat wins. All btc disappears into these black holes. We become rich, but we failed the world. Btc will be a settlement mechanism but not a currency. No one will care, node runners will quit, all nodes will be run by governments or etf companies, and they'll choose a ruleset to their liking. We get a CBDC. Humanity is enslaved... We're already enslaved, so I guess that's the point where we go full socialist and exterminate the leftover people.
There's only one way to get what we want, broadly speaking - we have to get the funds to pay out the btc. They can't be black holes.