I don't know that I would go quite that far. A blockchain is a linked list, but IMO a run-of-the-mill linked list doesn't quite make the cut to be a blockchain because I would argue that the essence of the word "blockchain" has to do with the "one block contains the hash of the previous block" property. A C-style linked list where the link is a pointer to a memory location would not be a blockchain.

That being said, I will definitely agree with you that the word "blockchain" is very overused and underspecified these days. Just because a term is often misused doesn't mean it has no definition. I think most of that is just laziness on the part of whoever is using it and not actual lack of...consensus...on a fairly clear definition.