Depending on the topic, a blog post can take me anywhere from 20 minutes to days to weeks. It's not as straight forward as people make it when estimating based on "time" and "effort" and you're right, the topics I post on actually are the sort of topics in industries where people get paid $50 or even $100 an hour.
Here is the point, some blog posts require a lot of research to put together, which can include reading books, academic papers, interviewing developers, and having the background to understand the topics. So are we moving away from the subjective theory of value and onto the labor theory of value?
What about people who post travel blogs which don't take a lot of academic research but because of subjective value get a high rating? So how exactly can we say for sure how much a blog post is worth objective? It's not possible, we can't, and we can't really go by salary or other standards.
A blog post is worth whatever it's deemed worth at the time by it's upvotes. The whole point of the upvotes and Steemit is to decide what they are worth because if we could decide without this process why do we need Steemit? Why not just hire bloggers on a salary?