It's certainly not necessary, it just provides specific advantages in terms of tamper resistance, validation, etc. If you're not working in a system where the integrity and authenticity is paramount and doing that validation over the wire constantly is prohibitive then there's no significant benefit. But there are lots of scenarios where those are EXACTLY what you want to prioritize. Several of the examples I added to my initial reply offer clear use cases that benefit.

As for my definition, I'll defer to the literal definition:

A blockchain is a decentralized, immutable digital ledger that records transactions chronologically in "blocks" linked together using cryptography. Each new block contains a hash of the previous one, forming a secure chain that is distributed across a peer-to-peer network of computers, making it tamper-evident and resistant to changes without network consensus. This distributed and transparent system eliminates the need for a central authority, allowing participants to verify and trust the recorded data.

Note that proof of work is NOT part of the definition. Proof of work is very specifically related to cryptocurrency, and exists only as a mechanism to prevent the arbitrary creation of additional currency (blocks). There is nothing about blockchain that requires proof of work. Often you use proof of stake instead of proof of work, but even that isn't strictly necessary

P.s. this is exactly what I mean when I talk about how grifters have ruined a perfectly good technology by poisoning the public awareness of it. The fact that you considered proof of work to be a core element of blockchain is because of cryptocurrency, and the notoriety it has received because of the grift. Other examples of this phenomenon include Tesla and their impact on the perception of autonomous vehicles (which Teslas are not, but try very hard to make you think they are), and LLMs and "AI" and their impact on the perception of real AI projects and other forms of machine learning.

Blockchain itself is just, at its core, a method of cryptographically proving the authenticity of a ledger history. That's it. What you DO with that technology is fairly boundless. You can embed anything in a block on the chain. We have lots of existing ways to handle proof of identity that can be inserted into a block (imagine if blocks contained the public key of block's creator and then the entire block (including the public key) is signed with the private key)