Isn't the power of blockchain coming from decentralization instead of immutability of blocks?

Question

I've only started exploring the working of blockchain. So what I've gained from guides on Google has me into thinking that what makes blockchain records resilient to corruption is distributed storage, because altering blocks on one or two nodes isn't going to make any changes in the collective decision of other nodes on some transaction. Like, other nodes would just reject the decision of such nodes because the majority of the same don't agree with it. Also, it's almost impossible for anyone to get to change records on the majority of nodes because alteration of blocks can only happen when the exploiter has direct access to records on the node, otherwise blocks are not even meant to be altered, so there is no other mechanism to change blocks' data than accessing all of them.

Does it mean that immutability of blocks that comes by virtue of linked hashing is of no use in providing secure transactions? On every other blockchain guide, it's been stated that blocks' data can't be modified because the hash of that block would change and all subsequent blocks would require changes which is not possible. But what confirms consistency between hash of blocks is by mutual agreement by other nodes. Otherwise if someone changes data on a block on some node, what prevents it even if chain of subsequent hashes is not making sense?

Answer 1

One important aspect of the Bitcoin blockchain is that each node independently makes its own decisions about which blocks it accepts. It does not depend on any kind of majority voting process. To make a decision, a node does not need to know what the majority of other nodes have decided.

The Bitcoin blockchain is not completely immutable. Individual blocks cannot be altered but at (or very near) the top of the chain, a block can be replaced by a different one with the same antecedent. This is necessary because there has to be a way to arrive at a common ordering of transactions in circumstances where two or more new blocks with the same precedent block may be produced at the same time but in distant parts of the network. Some nodes may receive one block before the other and other nodes vice versa. As new candidates arrive, nodes will throw out a previously accepted block or a few and replace it with an alternate set of blocks that represent more work having been done. This is block reorganisation at the tip of the chain. Short reorganisations of one or two blocks occur relatively often.

Consistency between nodes comes from applying the same rules concerning block and transaction acceptance. It is not a consultative process.

Linked hashing is an essential part of this process and is vital to the security of transactions.