Blockchain have to solve immutability and double spend, it is just sync of history of txes. It just need a rules written in code, there is no dependency on something called proof of work, proof of work is just an idea. Many nodes can sync and accept longest block without proof of work. Proof of work is just a proof of money and not proof of someone having brain or enough intelligence to protect chain security.
Discussion
proof of work and the nakamoto heaviest chains wins consensus enable a fully decentralized distributed database
that is, the number of candidates to be "leader" of the network is basically unlimited, and up to 50% of the network participants can be MALICIOUS
the Practical Byzantine Fault Tolerant 2/3 consensus mechanism, and can only tolerate 1/3 being MALICIOUS and it cannot scale beyond about 100 nodes before the cost of communication starts upwards like a classic exponential hockey stick expansion towards infinity
it is highly specious to say that this mechanism is decentralized compared to the nakamoto consensus based on proof of work hash difficulty adjustment
nakamoto consensus is more than orders of magnitude more decentralized
it's like comparing a small town of 3000 people with tokyo and saying "they are both cities"
there is in fact no practical limit to the number of participants in the bitcoin consensus, we are up to about 1/4 of the bits being zeros in the hashes and each new bit is more than the log10 expansion versus the previous added zero
bitcoin consensus could include the entire world population and still have room for expansion in the bazillions more