No it isn't. Because by design their holding has no bearing on your stack. They can't control shit and the vast majority of supply is already in circulation. The protocol does not care for the custodians. That is a decision on the individual user.

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I don't need to convince you of any of that, because simply: if all of what you said was to happen, the cypherpunks would just fork from a previous unspoiled Core version. Your stack is safe. It's the safest it can be. By design.
Even further, like what happened with BTC cash, the ensuing dump on their fake corn would make your stack even bigger.