A blockchain is a chain of blocks. Tautological, but the words mean something; it isn't just a name. If you hash blocks that contain hashes of previous blocks, you have a blockchain.
At most it might be argued that a centralized blockchain has no reason to exist, but I doubt that's true.
No, it doesn't work like that. "Blockchain" is understood to mean something and you can't decompose the compound word and say "well, here's a block. Oh, and here's a chain. I guess this is a block chain." Your description, e.g., applies to a Merkle tree [0], which git uses, and was published in 1979. But no one has ever or will ever call it a blockchain.
Is a Ford F-150 that's been lit on fire a firetruck? How much straw is in a strawberry?
That might be a losing battle, but not sure the battle is over yet...
It wasn't- there's one mention of a "chain of blocks" in the white paper. The term "blockchain" appears to have been coined by Hal Finney.