To be honest, that doesn't prove why steem can be worth anything. Like money, all money can be created but not all money are valuable. I have one major issue with steem and prove of brain method and that is how does that translate to value. The prove of brain concept will only work if value is transferred from the creator to receiver. On steemit, it doesn't seem to be the case. For example, your post made $18.57STU(with a value of over US$100 at the time i am writing this), but it only has 48 views. No matter how many votes you have, this article only impacted maximum of 48 viewers. if that 48 viewers paid you this much, then you can say this post has this much value. Another way to justify its value is if this post helped advertisers to generate enough income from that 48 views to pay you this amount of money (or that advertiser value that much on those 48 viewers). Otherwise how would you justify the value of steem and prove of brain really works?
At least prove of work can use its cost to justify the value of verifying its transaction and that isn't really a good justification in my option.