Software Engineering is actually about how things work and interact with people. I am sure most people know one part :)
Well, I lead a graphene blockchain developers at work & is working on cross chain technology for last 2+ years.
Not all the witnesses are programmers. @blocktrades is a veteran programmer, @anyx (is an academic as well), @netuoso are programmers. There could be other programmers as well. Most of the top witnesses like @gtg, @drakos etc posses excellent system administrator/security skills. I am not listing everyone but this is a list of people who are best of my knowledge closely associated with blockchain from a technology perspective. (This is not an exhaustive list)
Also, the skills for the Graphene (Bitshares/Steem/EOS) blockchain development is essentially C++ programming language and a library called BOOST. So in the above has people who work directly with C++ and BOOST libraries for more than 10 years.
The required skill setset would be - Approx 8 years of C++/BOOST expertise and a minimum 10 years of total software development expertise. (Obviously, this is my criteria and its highly subjective.). The total 10 years IMHO is highly required as that makes one humble as she will understand the silly issues associated with software development. Its not necessarily intelligence that matters but common sense and attention to things as opposed to focus.
Thanks a bunch for you highly substantive answer!