I work in security and I kinda doubt this. There are plenty of issues just like what is outlined here that would be much easier to exploit than social engineering. Social engineering costs a lot more than GET /secrets.json.
There is good reason to be concerned about both, but 95% sounds way off and makes it sound like companies should allocate significantly more time to defend against social engineering, when they should first try to ensure social engineering is the easiest way to exploit their system. I can tell you from about a decade of experience that it typically isn't.