As you know from what I said previously, I agree with you about the buyer you are referring to, the injustice of it all and I am surprised that CS don't remove the review.
However, I also believe that not everything is fair in life, business etc. and that while getting annoyed and reacting as you have is normal, understandable and even therapeutic, if the situation is something that you have no control over and cannot change then there comes a point when you need to just say "Screw it" and move on. The internet is full of people like that guy, you will likely have to deal with more of them down the line and that is whether it is on another freelance site or through your own website. If someone gives you an unfair review on Yelp or somewhere, what could you do about it?
I mean this in the nicest, most sincere and helpful way - Get over it. This is not helping you.
That review will not affect you, it will soon be lost among positive reviews and even if someone sees it by filtering for negative reviews it stands out as being ridiculous and the guy sounds like an idiot. It wont affect you.
The criticism of Fiverr is fair enough in a way but it should be viewed in the context that any other platform can be criticized for similar. There is very little difference in how these platforms behave in these circumstances and had this review been left on Yelp by a client from your own website it is unlikely that it would be removed. It makes sense to not have all your eggs in Fiverr's or anyone else's basket so do diversify, check out other options etc but remember that you have also had over 500 orders (I'm estimating) through Fiverr which did not go badly.