Actually you're not completely correct.
It's true Bitcoin is decentralized and anyone can own Bitcoin no matter what his country, ages, religions, etc. But there's a whale who own large amount Bitcoin in a single address, we also don't know how many address he have. If the large amount Bitcoin were moved to another address, it will be posted on whale alert and sometimes it's affect the market.
They (whale) may not controlling Bitcoin, but they've a big impact on the market.
If this were to happen, it would be a huge shock to bitcoin and all altcoins. Whales may not fully control bitcoin, but they can manipulate the market very well and will have a huge impact on the price of bitcoin and all altcoins.
Ponzi husks are indeed centralized, and bitcoin is only used as a tool to make the ponzi scheme look attractive because it uses bitcoin which is of course decentralized and cannot be controlled by anyone.
Many ponzi projects do bullshit by using bitcoin or cryptocurrencies as a means to attract members.