It is not to long, but as long as the author thought it needed to be. The simple fact you mention, obviously is not thet known to people - that's why they write mails to him. And he wrote this post he can point them to now, so they learn too.
And it also is obviously necessary, because people expect private answers. And the also expect answers to emails. And that's totally ok, because it is ok to be wrong. It only becomes a problem, if they don't accept the answer they get including the link to that article.
I even think it is important, he wrote it. Not only as a release valve, but because a) we are talking about it and b) it can be part of educating the 'masses' on why some things are the way they are (or should be).
Anything which helps people learn something necessary is welcome. I cannot but support it. What I intended to say is: sometimes abstraction helps explaining things. I just tried to abstract what led him to say so many things. The problem with rants is that people usually do not realize they are the object of it.
As someone told me time ago, if you want to say something to someone who is misbehaving, do not use a public medium: everybody else will get the message but he won't.
The rant format definitely tends to cause its own problems.
I think it's all our job now to take (parts of) his points and apply them to support and help pages of projects. That's probably most effective way to trigger change in general behaviour.
And it also is obviously necessary, because people expect private answers. And the also expect answers to emails. And that's totally ok, because it is ok to be wrong. It only becomes a problem, if they don't accept the answer they get including the link to that article.