It is definitely a big concern.
If countries or powerful people accumulate too much power, it defeats the purpose of bitcoin. The real purpose was to empower poor and weaker sections of the society. But if powerful have most of the bitcoin, they will become powerful and weaker section will suffer more. There is an additional concern that rich might be accumulating with different identities.
No. The real purpose was to grant self custody. The ability not to rely on a third party after the financial crisis of 2008.
Hence Decentralization
The purpose of Bitcoin is defeated when it is used through a third party or requires a third party
Like one is using a Bank.