So I uploaded 5 decent images of hatsune miku, and they were removed because they "weren't relevant to the site" http://prntscr.com/5zbrbw

How are they "not relevant"?

It's a character that's on here already.
You allow humanized and even have a "not_furry" tag.
There are thousands of purely human images on the site.

Yet you allow tripe like 9/11 posts and memes.

Is there a list of yay and neigh list that states how this isn't allowed or are the moderators just clueless?

https://e621.net/wiki/show?title=avoid_posting

Content that is not furry or furry-related. We may still approve it if it's high quality or "special" in some way, but it's still more likely to be deleted than approved.

Also there is stickied forum thread about this:
forum #146158

Oh look, the answer is in the third thread at the top of the forum front page.

NotMeNotYou said:
Oh look, the answer is in the third thread at the top of the forum front page.]
https://e621.net/post/show/19762 Silly me.

You'll notice that the thread is from only one month ago. The image you linked is from six years ago.
The policy (which I do agree with) is pretty new, but it was decided not to remove previously approved irrelevant posts.

Old posts won't be deleted, the not_furry rule has been in full enforcement for about a month for now, but everything you are searching are already posted on the thread that the other 2 users posted here.

That 9/11 picture you posted as an argument was posted 6 years ago when the not_furry rule wasn't applied so strictly.

boopboop said:
https://e621.net/post/show/19762 Silly me.

Same thread.

And as it was said above, your "argument" is 6 years old, approved under the rule of the very first lead admin, and we're currently at number three.

Also, I go out on a limb and say that the forum post of the current lead admin carries slightly more weight then a 6 year old post.
But, what do I know?

boopboop said:
Yet you allow tripe like 9/11 posts

I am shocked!