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Re 1: Many aspects are fairly centralized. Each individual aspect also entails risks.

A) The hashpower: The two largest mining pools control 53% of the hashpower. The top five mining pools control 82% of the hashpower. Source: mempool.space

B) Bitcoin trading: A few exchanges control the majority of global trading volume. Source: coinmarketcap.com

C) Ownership: Satoshi has about 5% of the BTC supply. Institutional Bitcoin holding is growing. The top 100 addresses control approx. 9% of the available BTC. Source: coinlore.com richlist

D) Mining hardware: There are only 3-4 relevant Bitcoin mining hardware manufacturers, of which Bitmain is by far the leader. Most large pools are probably used by Antminer. I could not find any reliable figures on this.
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@Gernhard_Reinholzen
About the mining pools:
The mining pools are service providers that merely bundle the hashrate of the miners and distribute the block rewards. The actual power lies with the miners themselves, as they can change the pool at any time if it acts against the interests of the network (e.g. in the event of a 51% attack or the censorship of transactions). Historically, there was a case in 2014 where GHash.io reached over 50% of the hashrate, but the community reacted quickly and miners switched to other pools. After all, no miner is interested in destroying their own business model :)

Trading volume on exchanges:
Exchanges have no influence on the decentralization of the network, as Bitcoin can be traded peer-to-peer - without central platforms. Exchanges can fail or be abused, but this has no impact on the integrity of the network itself. Bitcoin remains independent no matter what happens to the exchanges. FTX sends its regards haha😂

On ownership:
Unlike Proof of Stake, there are no additional rights for large holders in Bitcoin. Regardless of whether someone owns 0.001 BTC or 1,000 BTC - the protocol treats everyone equally. Wealth does not confer any power over the network, which makes Bitcoin fundamentally different from other projects such as ETH.

Mining hardware:
It is true that a few companies like Bitmain dominate the manufacturing of mining equipment. However, this does not affect decentralization, as miners have the freedom to choose their hardware and new market participants are constantly entering the market. Competition is also forcing manufacturers to be transparent. Bitmain, for example, has disclosed parts of its code in order to create trust. Even in the unlikely event that a manufacturer installs a backdoor, the network would only be affected in the short term, as other miners could quickly close this gap.
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