In general once a site has reached large enough size, most posts get voted to close by the community, or flagged by the community for closure or deletion. And on Music.SE this works really well for almost all posts. And I agree with Todd on this - this is what we as mods want, as it saves us effort, and allows us to focus on the more complicated things we need to do. I also agree that this is the place to raise discussion about it.
But there are certain actions which mods absolutely have the power, and the right to do summarily, is to delete posts which are offensive, spam and a few other reasons.
For spam and offensive posts we delete, and even remove accounts as quickly as we can see them.
With off topic questions we generally can leave them up to the community, or what I try and do is wait until 4 votes to close have been passed, so I can act as one vote, rather than as a unilateral close.
But an exception is with questions that are not a good fit here, but that will attract a lot of activity. For these we also are likely to delete rather than put on hold, as we don't want people to have to put in effort answering a post that will be deleted. It's just not good for anyone. It is not one that could simply be edited to make it work -
Now - this specific post mentioned is explicitly off topic for this site. There is no doubt about that. Yes, the writer obviously put a fair amount of effort into writing it and the answer, and in terms of detail, I like what he's done. I would read it if it was on a blog.
But it is suitable for a blog. Not here.
Unfortunately the structure of it also means it is not something you could ust edit to make it fit, without deleting the answer anyway.
I'd second @Todd's comment to Marko about reading the FAQ to see how the site works. It looks like that is where the issue lies. And I absolutely approve of him raising the question here in meta to get community input.