Jonita answered with:
The best approach to this would have been to kill it early. Ignore the fact that the title is a reasonable question, deal with the fact that the content is a rant by closing the question. Instead of saving the question, create a new one with a neutral content that brings out the same information.
I disagree with this. I think there's an interesting point to the question (which is why I decided to answer, and people seemed to like that seeing the up votes).
So yes, it could have been killed early, then the asker would have learned nothing and the useful answers that there are now, albeit to a slightly different question, wouldn't have been there either.
In the end, I think we're better off as it is, with the question slightly different (or as I'd prefer to say: optimised to suit this site).
In your question, you mention:
Not hijaking someone else post is one of the basic rules of the SE network. Why has this been allowed in first place?
Indeed, that's a bit of a trade-off. Sometimes, it's suggested to closed the bad question and ask it yourself (as a more experienced user) if you're interested.
I don't think that's very welcoming. Indeed, the original asker came up with the novel (at least on this site) idea for a question and then some other user decides it's not good enough and gets the credit for it.
Ideally, the question is edited with a comment to the original author that it's better that way. They still get credit and the question is better, hopefully allowing them to learn and become more involved with the site by coming up with more questions.
In this case, I recognise that there have been some unfortunate edits by the original author that didn't improve the question. Seeing that the question was good at some point, I think that's the ideal place to stop editing. Edits should only be made to improve a question and I would support a moderator fixing it if edits are contested or an edit war is happening.
In this case, that could have been done, but now it seems the edits have stopped and the current version seems good (to me at least). As such, the end result is good, but the way there was a bit bumpy. Not ideal, but we're better off than not having the question (and more importantly the answers that followed) at all.
Now, for some of your points, I'll also provide a reply.
The OP officially asking for the question to be deleted, and being completely ignored
This isn't really a problem. The OP and the editors have licence their content with Stack Exchange. It's now available licensed as CC-BY-SA and that means that you as author can't prevent others from presenting the content under the terms of that licence. In particular, it means you cannot force Stack Exchange to remove your content. The best you can do is ask for account disassociation, so the author will change to something like
OP ranting in comments everywhere
These can just be flagged. There is no exceptional position here allowing anyone to do that. If you think it's inappropriate, flag it accordingly.
Other users complaining with the OP for constantly rewording the question, which is perfectly fine instead if you consider OP never asked the question
This can be a bit tedious indeed. Eventually, it's best to ask on Meta to get consensus in the community. In that regard, you did an excellent job listing all the points that bothered you (and others).
A list of other answers which are not answering the question at all in the new version because, quote: <> and none of the answers quote anything like that. All answers are clearly opinion based.
I think this was in some of the older versions as well. It's not necessarily a problem because a whole bunch of countries signed that. For example, my answer provides a reason from Vietnam officials (Vietnam is a party to the convention) and the WWF (an environmental group). And some other answers mention Australia, New Zealand, PETA and the IWC (which is aimed at conservation to have sustainable whaling). So I don't really agree with this assessment. Not everything in all the answers is well referenced, but many arguments, even many referenced ones, are useful.